[JakeGinnivan]

Summary

Start the migration to standard Temporal values without extending the Luxon interface. Stacked on #210; the shared conference-config/provider contract remains unchanged in this first slice.

conferenceDate(ISO date) -> Temporal.PlainDate
conferenceTime(ISO datetime) -> Temporal.ZonedDateTime
                         configured IANA zone by default
Temporal.Instant         exact timestamps and provider epoch values

Use native Temporal where available and temporal-polyfill 1.0.6 elsewhere, without installing globals. Reject ambiguous/nonexistent wall times unless a caller explicitly selects a disambiguation policy.

Migrate talk-end checks and run-sheet highlighting calculations, remove redundant timezone arguments at feature call sites, and extend provider lint to reject direct Temporal.Now reads. Add lasting usage guidance and a reproducible pnpm nx temporal-check website compatibility/bundle check.

Evidence

• Before: the local Workers runtime does not expose native Temporal, and shared parsing returns Luxon objects.
  After: native Node Temporal, forced fallback, and Workers return identical date/instant/DST results. React SSR hydration agrees in Chromium, Firefox, and WebKit, both with normal support and native Temporal explicitly disabled.
• 96 test files / 887 tests pass, including configured zones, offset preservation, date-only values, DST gaps/overlaps, serialization, migrated feature behavior, and provider lint.
• Production build, typecheck, and lint pass. Lint retains two warnings in generated Wrangler types.
• The compatibility target prints isolated minified/gzip bundle measurements for equivalent Temporal and Luxon date operations. These are dependency comparisons, not whole-site savings while both libraries coexist.

Merge Danger

Door: two-way

No persisted data or config schema changes. Standard Temporal types are introduced at a small module; the remaining Luxon contract can migrate in subsequent PRs.

Blast Radius: timing

Talk feedback availability and run-sheet timing now parse through Temporal. Invalid timestamps retain their existing feature-specific fallback behavior. Offset-free ambiguous/nonexistent wall times are rejected rather than silently normalized. The native fallback adds client payload on migrated routes until the remaining Luxon usage is removed.