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

tests/unit/services/MeetingService.test.ts

@@ -91,6 +91,7 @@ describe('MeetingService', () => {
       }).meeting;
       // 新しいミーティング(10:30-11:30)は重複
       const conflicts = service.checkScheduleConflicts(
+        authorId,
         projectId,
         [memberId],
         '2026-06-15T10:30:00',
@@ -109,6 +110,7 @@ describe('MeetingService', () => {
         memberIds: [memberId],
       });
       const conflicts = service.checkScheduleConflicts(
+        authorId,
         projectId,
         [memberId],
         '2026-06-15T11:00:00',
@@ -125,6 +127,7 @@ describe('MeetingService', () => {
         memberIds: [memberId],
       }).meeting;
       const conflicts = service.checkScheduleConflicts(
+        authorId,
         projectId,
         [memberId],
         '2026-06-15T10:30:00',
@@ -144,6 +147,7 @@ describe('MeetingService', () => {
         createdById: memberId,
       });
       const conflicts = service.checkScheduleConflicts(
+        authorId,
         projectId,
         [memberId],
         '2026-06-15T10:30:00',
@@ -169,6 +173,7 @@ describe('MeetingService', () => {
         orderIndex: 0,
       });
       const conflicts = service.checkScheduleConflicts(
+        authorId,
         projectId,
         [memberId],
         '2026-06-15T10:00:00',
@@ -194,6 +199,7 @@ describe('MeetingService', () => {
         orderIndex: 0,
       });
       const conflicts = service.checkScheduleConflicts(
+        authorId,
         projectId,
         [memberId],
         '2026-06-15T10:00:00',