feat(alarm): multiple alarms (US-001)

[Hectormalvarez]

Summary

Implements US-001 (Multiple Alarms) per docs/stories/US-001-multiple-alarms.md:

• New alarm feature module (pure core + storage adapter + UI), mirroring the timer feature pattern
• Create/name/enable/disable/delete alarms; one-shot firing with 9-minute snooze
• Alarms persist across reloads; ring only while the page is open (limitation shown in-panel)
• Ringing overlay with Snooze/Dismiss, keyboard dismissal (Esc/Enter)
• 40 new alarm unit tests (135 total); full QA assessment passed; code review approved

Also includes two chore commits from IDE tooling (.clinerules files) and story/readme docs.

Test plan

• npm run typecheck / lint / prettier --check
• npm test (135 passing, incl. adversarial reload-mid-minute, snooze-expiry, grace-window boundary checks)
• npm run build