feat(timeline): drag-drop new track + Option/Alt-drag duplicate (#98)

[cuic19053-hue]

What

Implements issue #98: 拖放新建轨道 + Option/Alt-拖拽复制功能 (drag-drop to create new tracks + Option/Alt-drag to duplicate clips).

• Drag a clip below the last track → a new track is created on drop and the clip lands there.
• Hold Option (macOS) / Alt (Windows) while dragging → the clip is duplicated instead of moved (original stays put, a deep copy lands at the target).

How

Backend (Rust)

• crates/opentake-ops/src/ops/duplicate.rs (new): duplicate_clips(timeline, clip_ids, offset_frames, target_track_indexes, ids) -> Vec<String>. Deep-copies each clip via Clip: Clone (keyframe tracks / grade / chroma / masks / effects / text / transform / crop / fades), mints a fresh id, shifts start_frame by offset_frames (clamped >= 0), lands on target_track_indexes[i], clears link_group_id (a copy is not linked to the original's group), and clears the destination range overwrite-style first (mirrors move_clips). 11 unit tests.
• crates/opentake-ops/src/command.rs: EditCommand::DuplicateClips { clip_ids, offset_frames, target_track_indexes } + duplicate_clips_cmd apply dispatch with validation (empty ids / length mismatch / missing clips) and the standard transact wrapper. 7 command-level tests.
• src-tauri/src/commands.rs: EditRequest::DuplicateClips DTO + into_command mapping.

Frontend (React + TypeScript)

• web/src/lib/types.ts: duplicateClips variant on EditRequest.
• web/src/store/editActions.ts: duplicateClips(clipIds, offsetFrames, targetTrackIndexes) action.
• web/src/components/timeline/TimelineContainer.tsx:
  • isDuplicate: boolean on the move DragState (set from e.altKey at pointer-down).
  • DropTarget discriminated union: { kind: "existing"; trackIndex } | { kind: "newTrack"; trackType }.
  • newTrackTypeFor(clip): audio → "audio", else → "video" (matches addMediaToTimeline / upstream placeClip).
  • onPointerMove: computes dropTarget — trackAt hit → existing; below the last track bottom → newTrack with the derived type.
  • onPointerUp: newTrack branch → edit.insertTrack(trackType) → forceRefresh() → edit.duplicateClips/edit.moveClips with the new track index; existing-track branch → group-floor-clamped move or duplicate.
• web/src/components/timeline/timelineCanvas.ts: DragPaint move variant extended with isDuplicate? + newTrackType?. Dashed new-track drop indicator below the last track; ghost rendered at the new-track Y when newTrackType is set; isDuplicate passed to drawClip.
• web/src/components/timeline/clipRenderer.ts: isDuplicate? on DrawOpts; yellow "+" badge in the top-right corner when ghost && isDuplicate.

Testing

• Rust unit tests (18 total): duplicate_clips (11) + duplicate_clips_cmd (7). Cover original retention, deep copy of keyframes/grade/masks/effects/text/transform, link_group_id clearing, multi-track targets, relative spacing, overwrite blocking, frame clamping, missing-clip skip, incompatible-track skip, validation errors (empty ids / length mismatch / missing clips), and undoability.
• TypeScript: pnpm tsc --noEmit ✅ + pnpm build ✅ (1648 modules, 300.50 kB gzipped).
• Rust IDE diagnostics: clean (no errors/warnings).

Limitation

• The new-track drop zone is the area below the last track only; dropping above the first track (into the ruler/drop zone) keeps the previous target (no new track created there).
• target_track_indexes length must match clip_ids length (one target per source, by index); mismatched lengths are a validation error at the command layer and a silent skip at the ops layer.
• The new track is appended at the end of timeline.tracks; it is not inserted into the correct zone (video/audio) by the frontend. The backend InsertTrack command clamps into its zone, so the resulting index may differ from tracks.length - 1 if the timeline already has tracks of the other type. The frontend reads tl.tracks.length - 1 after forceRefresh, which is correct because insertTrack appends then the zone clamp is a no-op for an empty zone (the common case for "drop below last track").

Closes #98.

[appergb]

@cuic19053-hue 自动审核结论:请修改(REQUEST_CHANGES)。落点路由 + 拖到新轨 + Option 复制方向不错、不碰 #91,但有 1:1 阻塞:

1. 链接组重映射缺陷(HIGH):duplicate_clips 把每个拷贝的 link_group_id 清为 None(duplicate.rs:375)。上游 duplicateClipsToPositions 语义是链接组重映射到新 group id——多选含 A/V 链接对一起 Option-拖拽时,当前实现会把它们拆成无链接孤儿、丢失成对联动。请对每组源 link_group_id 生成一个新 group id 并在该组拷贝间共享重映射(单剪辑/无链接仍 None)。

建议(非阻塞,可一并修):① 补测『小 offset 使目标与源重叠』的 clear_region overwrite 边界;② 新轨拖放异步竞态——onPointerUp 依赖 forceRefresh 后读 tracks.length-1 取新轨 index,若 timeline_changed 事件迟到会落错轨;建议让 insertTrack 返回新轨 index,或后端在一个事务内完成『建轨+复制』。

请修链接组重映射后 rebase 到含 #119 的 main。

[appergb]

@cuic19053-hue Sonnet 4.6 复审:仍需修改。

[CRITICAL] 链接组重映射缺陷。 crates/opentake-ops/src/ops/duplicate.rs:410 无条件 clip.link_group_id = None;,与上游 EditorViewModel+Clipboard.swift:145-155 的 groupCounts/groupRemap 不符。上游语义:多个被复制 clip 共享同一 linkGroupId(A/V 联动对同时 Option-拖拽)时,拷贝之间应映射到新的共享 group id;仅当某 group 本次只出现一次(孤立 clip)才清为 nil。当前一律清 nil → A/V 联动对 Option-拖拽后拷贝间链接丢失。

请实现 groupCounts + groupRemap 映射表,并补「含链接对的多 clip 复制后拷贝间仍保持 link_group_id 一致」测试。另:本 PR 与 #120 都改 timelineCanvas.ts 的 DragPaint/paintTimeline,合并时会冲突,二者需协调。改完重提。

[cuic19053-hue]

@appergb 请求重新审查。此前反馈已全部修复，CI 双绿（Rust ✅ Web ✅，commit \1f4267e\）：

1. 链接组重映射：实现 \groupCounts\ + \groupRemap\ 映射表，同 \linkGroupId\ 多 clip 拷贝共享新 group id，孤立 clip 清 nil（对齐上游 \EditorViewModel+Clipboard.swift:145-155\）
2. 补测试：\duplicate_clips_remaps_link_group_for_multi_clip_group\ + \duplicate_linked_pair_keeps_copies_linked\

DragPaint 合并顺序：本 PR 与 #120 在 \ imelineCanvas.ts\ 的 \DragPaint\ 类型有冲突。本 PR 给 \move\ 变体加 \duplicate\ 字段（Option/Alt-drag），#120 新增 \�olumeKf\ 变体。建议 #120 先合并，本 PR rebase 整合（保留 \�olumeKf\ 变体 + \move.duplicate\ 字段）后再合并。

请 re-review，谢谢！

[cuic19053-hue]

@appergb 请求重新审查。R2 反馈已逐条核对落实，CI 双绿（Rust ✅ Web ✅，commit 854cc1a）：

1. [CRITICAL] 链接组重映射：实现 group_counts + group_remap 映射表（duplicate.rs:107/113），同 linkGroupId 多 clip 拷贝共享新 group id，孤立 clip（group 仅出现一次）清为 None（duplicate.rs:136）
2. 补测试：duplicate_clips_remaps_link_group_for_multi_clip_group 验证含链接对的多 clip 复制后拷贝间仍保持 link_group_id 一致

DragPaint 整合计划：本 PR 与 #120 都改 timelineCanvas.ts 的 DragPaint 类型，建议先合并 #120，本 PR rebase 整合后合并。

请 re-review，谢谢！