Fix dashboard plan sync and unify inline playback controls

[Talljack]

Summary

• persist content snapshots when saving built-in wordbook practice so book-based Today's Plan tasks can sync completion correctly
• unify desktop Web playback UI so listen/[id], read/[id], and wordbook practice use inline read-aloud controls while iOS native keeps native controls
• add regression coverage for Today's Plan sync and inline playback controls

Verification

• pnpm vitest run src/__tests__/daily-plan-progress.test.ts
• pnpm playwright test e2e/listen.spec.ts --grep "listen detail page has playback controls"
• pnpm playwright test e2e/read.spec.ts --grep "read detail page shows stable practice controls without transcript card"
• agent-browser manual QA:
  • completed write/book/daily-vocab?limit=3 and confirmed dashboard Today's Plan changed to 1/4 completed
  • verified listen/listen-1 shows LISTEN CONTROLS inline under content
  • verified read/article-1 shows READ CONTROLS inline under content

[vercel]

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Project	Deployment	Actions	Updated (UTC)
echo-type	Ready	Preview, Comment	Jun 12, 2026 1:30am