Keep Daily day transitions on the horizontal axis

[cameronapak]

Summary

Daily day switches keep the active pill inside the calendar strip and move it only on the horizontal axis, even when the outline is scrolled.

Changes

1. Day transitions avoid scroll-sensitive shared-layout projection by handing the current horizontal offset to the destination pill.
2. Async navigation is latest-wins and discards stale, cancelled, reduced-motion, and paged-away handoffs.
3. The subheader opens at its natural measured height so day remounts do not collapse or bounce the calendar band.

Screenshots

• Before: reported scroll bounce
• After: verified recording and review thread

Flow

flowchart LR
  A[Click day] --> B[Get or create day]
  B --> C[Guard latest request]
  C --> D[Measure painted x delta]
  D --> E[Open destination]
  E --> F[Run x-only tween]
  F --> G[Clear on end or cancel]

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Test plan

• bunx playwright test e2e/week-calendar.spec.ts --workers=1 - 13 passed
• bun run typecheck && bun run typecheck:test && bun run typecheck:worker
• bun run lint && bun run fmt:check && bun run check:docs && git diff --check
• bun run check:changeset

[pullfrog]

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