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

app/api/projects/[projectId]/meetings/[id]/route.ts

@@ -61,6 +61,7 @@ export async function POST(
   const service = createMeetingService();
   try {
     const conflicts = service.checkScheduleConflicts(
+      user.id,
       Number(projectId),
       Array.isArray(body.memberIds) ? body.memberIds.map(Number) : [],
       String(body.startAt ?? ''),