Phase-1 base: Avalonia migration spine (UIMode defaults Legacy)

[johnml1135]

Phase-1 base: Avalonia migration spine

First of a 4-PR stack landing Phase 1 of the WinForms→Avalonia migration. Every Avalonia surface is gated behind the UIMode setting, which defaults to Legacy (Src/Common/FwUtils/Properties/Settings.Designer.cs) — so default users see no change.

What this PR contains

• The Avalonia migration framework: region/composer (FullEntryRegionComposer), view-definition IR, owned controls, seam contracts, plugin registry.
• The base detail-editor surfaces active under UIMode=New: lexiconEdit, lexiconEditPopup, notebookEdit, posEdit.
• The browse table view code (LexicalBrowseView, LexicalBrowseHostControl, BulkEditBarView, ClerkBrowse*) and its RecordBrowseView wiring — shipped dormant (it's fused to base wiring and can't be cleanly carved out; activated by the table follow-up).
• Skills/infra and the roadmap's core proposal/design/tasks/spec, plus the landed openspec change specs (lexical-edit-avalonia-migration, shared-editable-virtualized-table, avalonia-multi-writing-system-text-foundation) — pared back from the original diff (see "Branch cleanup" below).
• Back-out of 4 cleanly-removable unwired Avalonia dialogs (SpecialCharacter, WritingSystemProperties, DeleteConfirmation, LexReferenceDetails); 13 dialog UIs + a shared MessageBox ride behind UIMode=New, each verified wired to a real WinForms call site.

Inert follow-up surfaces

The interlinear and rule-formula detail editors are carved out to the stacked follow-up PRs below (their openspec proposals and view files are not in this PR). The browse table and ChorusNotesBarControl (the Chorus/FLExBridge notes bar) ship here but inert. The inert lists are LexicalEditSurfaceRegistry.Phase1FollowUpSurfaceTools and LexicalEditSurfaceResolver.Phase1FollowUpBrowseTools; the migration skill documents the activation recipe.

Stack (each merges into the one above)

1. this → main
2. phase1-followup-interlinear → phase1-base
3. phase1-followup-rule → phase1-followup-interlinear
4. phase1-followup-table → phase1-followup-rule

Migration per-screen docs (the basis for JIRA tickets) and the full 13-stage migration-program planning material (speculative future-phase work, not needed to review this PR) both live on the separate, never-merged phase1-docs branch (draft PR, explicitly marked do-not-merge).

Verification

Whole-solution build green. Surface-registry census: 6 custom-slice classes classified (LexemeEditorBurnDownTests); 7 tools in LexicalEditSurfaceRegistry.Phase1FollowUpSurfaceTools; 8 tools in LexicalEditSurfaceResolver.Phase1FollowUpBrowseTools. Full CI-equivalent test run passes except 38 pre-existing, environment-specific test failures unrelated to this branch (a cross-worktree test-data collision, fixed separately in #979). Note: two of the hardening test files (RegionCommandAdapterHardeningTests.cs, RegionObjectCommandExecutionTests.cs) run roughly half their cases only on the manual [Explicit] desktop lane, not CI — "tests added" for these files should not be read as "tests running in CI." Draft until the stack is reviewed top-to-bottom.

Branch cleanup (post-review)

A multi-part internal review of this branch (PR_964_review.md, not included in this diff) found and fixed a substantial amount of unrelated or stale content bundled into the original diff. Squashed into this single commit; highlights:

• Removed content unrelated to the Avalonia migration: an unrelated installer-docs deletion and an ungated Legacy-mode rendering change were reverted, and a misplaced/stale stray doc file was dropped.
• Split two unrelated-but-legitimate fixes into their own PRs: #978 (VersionInfoProvider copyright/version-string bugs, a stale RegFree.targets entry, an opsx-prompt refactor) and #979 (a pre-existing cross-worktree test-collision bug in RealDataTestsBase, found while verifying this branch but unrelated to it).
• Fixed a real build break (RecordBrowseView.cs used a pub/sub API signature main had already replaced) and a real product bug (the Avalonia refresh controller could stay unwired when a tool loads directly into UIMode=New) — and the test proving it (RecordEditViewSwitchTests) is now green: the shared idle-queue test-drain helper had never actually worked in this environment (it reflected into a private method whose message-pump politeness check always aborted), which also meant 5 test fixtures weren't proving what they looked like they proved. Centralized a correct drain in XWorksAppTestBase, which surfaced and fixed a second bug (2 fixtures missing a layout/parts Inventory bootstrap 2 sibling fixtures already had). All affected tests pass; full xWorksTests suite: 1645 passed, 0 failed.
• Pared back ~7,500 lines of speculative future-phase openspec planning docs, deleted two fully superseded proposals and stale datatree-model-view-separation specs asserting an architecture that was never built, and removed remaining POC/spike language and stale cross-references repo-wide (including a real stale-default-value bug in Run-AvaloniaPreview.ps1).
• Gated ChorusNotesBarControl as a Phase-1 follow-up surface (it was live, contradicting its "dormant" framing); wired the one missing UIMode gate (GoLinkEntryDlgListener.OnGotoLexEntry); documented one honest parity deferral (MsaInflectionFeatureListDlgLauncher switch-tools navigation); removed dead API and ~20 orphaned localization keys; strengthened the FwAvalonia engine-isolation audit to match its own documented symbol list; fixed three evidence-language issues in Path3BundleTests; reconciled dialog spacing tokens against real measured WinForms control geometry.
• Code coverage review: ran line-level coverage analysis across the PR's own added code, found and closed the highest-value real gaps (35 new tests total: MSA-launcher resolver switch/not-found branches, ApplyInflectionFeatures's undo-task-safety null guards, an XmlViewsUtils part-ref regression test, and the pure/testable logic across all remaining under-tested Lcm*Launcher classes), and documented the genuinely modal-locked gates that can't be unit-tested without a production testability seam. Full breakdown below.

9-group breakdown: scope, gaps found, what was fixed vs. left as a finding

Every file in this PR's diff (562 files) is accounted for in exactly one of the 9 groups below (verified programmatically — zero unclassified). Full detail, file-by-file evidence, and exact test names are in PR_964_review.md §18.

#	Group	Files	Scope	Gaps found	Fixed	Left as a finding (owner decision needed)
1	Avalonia core framework — Src/Common/FwAvalonia/{Region,ViewDefinition,Seams,Preview}/, root FwAvalonia/*, FwAvaloniaPreviewHost/	84	The framework substrate: XML-to-IR compiler, composer/render layer, framework-neutral seams, preview host	3	1	Preview/ code ships inside the production DLL (excluding it would break FwAvaloniaPreviewHost.exe's current project-reference wiring, a build-topology change); FwAvaloniaStrings.resx has orphaned keys (deleting/rewiring changes shipped localization surface)
2	Avalonia framework + dialog tests — FwAvaloniaTests/, FwAvaloniaDialogsTests/, RenderTestInfrastructure/, RenderVerification/	100	4-tier test suite: unit, headless-UI, visual/snapshot, parity-bundle	2	0	Extracting a shared AvaloniaHeadlessDialogFixtureBase (~24 files) and a shared ViewDefinitionModel test-builder (~9 files) are DRY/maintainability refactors of existing, passing tests, not coverage gaps; real but non-trivial regression risk, recommended as a dedicated follow-up rather than bundled in here
3	Avalonia dialogs (product) — FwAvaloniaDialogs/ (excl. tests)	71	MVVM dialog kit: 13 dialog UIs + shared MessageBox	0	--	--
4	Product wiring / integration — Src/xWorks/*.cs (excl. tests), Common/Controls/, Common/FwUtils/, Common/FieldWorks/, XCore/, Common/Framework/, Common/SimpleRootSite/, Common/ViewsInterfaces/	62	The highest-risk layer: where a Legacy regression would surface for existing users	3	3	--
5	Src/xWorks/xWorksTests	47	Test evidence for the composer/plugin-registry, the 4 active surfaces, the dormant browse table	2	2	--
6	Src/LexText — LexTextControls/, Lexicon/, Morphology/, Interlinear/, LexTextDll/	58	~45 if (UIMode==New) {Avalonia} else {legacy} dialog-launcher gates; 13 new Lcm*Launcher glue classes	1 (coverage)	1 (35 new tests)	3 modal-locked gate/dispatch sites (EntryDlgListener.cs, 3 gates; MSAPopupTreeManager.cs, 2 gates; LexReferenceMultiSlice.GetRootObject) — every path ends in a real modal dialog this codebase deliberately excludes from unit tests; fixing needs a production testability seam, a decision for whoever owns this PR
7	openspec — landed changes + roadmap core	95	The honest record of what shipped (11,321 of 11,993 lines); only 672 lines remain forward-looking, both substantially implemented	1	0	datatree-model-view-separation's one openspec validate --strict failure predates this PR entirely — not this PR's scope to fix
8	.claude/skills + .github	31	Migration hub skill, satellite review skills, dialog-authoring skill, MCP docs	0	--	--
9	Repo mechanics / misc — .sln/.proj/Directory.Packages.props/root docs	14	Mechanical project registration + package additions	0	--	--

Totals: 12 gaps found across the PR: 7 fixed (35 new tests + 4 doc/comment corrections), 5 left as explicit findings (2 production-restructuring, 2 test-refactor-only, 1 pre-existing-elsewhere) — none silently dropped.

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NUnit Tests

    1 files  ±    0      1 suites  ±0   14m 20s ⏱️ + 3m 41s
6 100 tests +1 801  6 019 ✅ +1 793  81 💤 +8  0 ❌ ±0 
6 109 runs  +1 801  6 028 ✅ +1 793  81 💤 +8  0 ❌ ±0 

Results for commit c37eb02. ± Comparison against base commit 323a022.

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