feat(m15): full test completion + quality gate + validation fixes

- Add E2E notifications.spec (member-added notification -> list -> mark read)
  and activity-log.spec (board_posted + todo_created recorded)
- Set Playwright workers=1 for deterministic full-suite runs (SSE test under
  parallel load); full E2E suite (18 tests / 13 specs incl. 12 mandated
  scenarios) green
- Quality gate: 251 unit/integration tests, lint clean, typecheck clean,
  build succeeds, coverage 91.13% Repository/Service (>=80%)
- Validation fixes (mandatory): SearchService now searches ALL items
  (large pageSize) instead of first page only; MeetingService.
  checkScheduleConflicts now requires membership (actorId) to prevent
  non-member info enumeration

playwright.config.ts

@@ -6,7 +6,7 @@ export default defineConfig({
   fullyParallel: true,
   forbidOnly: !!process.env.CI,
   retries: process.env.CI ? 2 : 0,
-  workers: process.env.CI ? 1 : undefined,
+  workers: 1,
   reporter: 'html',
   globalSetup: './tests/e2e/globalSetup.ts',
   use: {