Labels: good first issue, area:webui, area:testing
Difficulty: S (~1–3 hours)

Context

apps/webui/src/ui/notification-settings.ts persists the cockpit's notification
preferences to localStorage and is deliberately defensive: SSR, a missing
localStorage, and corrupt stored values must all degrade to the all-off default.
That coercion logic currently has no test coverage at all (no test file references the
module), so a refactor could silently break the safe-degradation behavior.

What to do

1. Read apps/webui/src/ui/notification-settings.ts (70 lines). Public surface:
   defaultNotificationSettings(), readNotificationSettings(),
   persistNotificationSettings(); internal coerceCategories().
2. Create apps/webui/test/notification-settings.test.ts. The webui test suite runs in
   a plain node environment (apps/webui/vitest.config.ts:16), so stub
   window.localStorage with a small in-memory object — copy the pattern from
   apps/webui/test/policy-cache.test.ts:28-51 (MemStorage + globalThis.window stub).
3. Cover at least:
   • no window (SSR path) → defaults, no throw
   • empty storage → defaults
   • round-trip: persistNotificationSettings(s) then readNotificationSettings() → s
   • corrupt JSON / non-object JSON ("42", "[]") → defaults
   • enabled present but not strictly true (1, "yes") → false
   • categories with unknown extra keys → dropped; non-true values → false
   • getItem / setItem throwing (private-mode simulation) → no throw, safe fallback

Acceptance criteria

• New test file passes: pnpm --filter @actradeck/webui test
• All bullets above are asserted (not just the happy path).
• No production code changes needed. If you find an actual bug while testing, report it
  in the issue thread instead of folding a behavior change into the test PR.
• Full gate green: pnpm type-check && pnpm lint && pnpm format && pnpm test