feat(alarm): recurring daily-repeat alarms (US-002)

[Hectormalvarez]

What

US-002: recurring (daily-repeat) alarms — story docs/stories/US-002-recurring-alarms.md (MVP scope: daily repeat only; weekday scheduling recorded as future work).

Core

• Persisted schema-additive flags: repeat + lastRungDay on Alarm; legacy JSON (no flags) normalizes to one-shot — no migration, no data loss
• Repeat alarms are never consumed by ringing: the ring consumes the local calendar day (lastRungDay), so a dismiss mid-grace-window or a page reload cannot re-ring the same occurrence; the next day rings again
• Toggling clears both markers (re-arms from the configured time); snooze interplay unchanged

UI

• "Daily" checkbox in the create form (label + focus ring per US-005 control language); resets after add
• Monochrome ↻ SVG indicator on repeat rows only (role="img" + aria-label "Repeats daily")

Verification

• 152/152 unit tests (12 new covering AC-2..AC-8 incl. next-day re-ring, legacy parse, toggle re-arm, second-due queuing); make check green
• 7/7 Playwright assertions (indicator on repeat rows only, flags persist to localStorage, checkbox resets); 2 screenshots in the story folder