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/e2e/activity-log.spec.ts

@@ -0,0 +1,49 @@
+import { test, expect } from '@playwright/test';
+
+function unique(prefix: string): string {
+  return `${prefix}-${Date.now()}-${Math.floor(Math.random() * 1_000_000)}`;
+}
+
+async function setupOwner(page: import('@playwright/test').Page) {
+  const email = unique('owner') + '@example.com';
+  await page.goto('/login');
+  await page.getByRole('button', { name: '新規登録はこちら' }).click();
+  await page.getByLabel('表示名').fill('Owner');
+  await page.getByLabel('メールアドレス').fill(email);
+  await page.getByLabel('パスワード').fill('password123');
+  await page.getByRole('button', { name: '登録する' }).click();
+  await expect(page).toHaveURL(/\/dashboard/);
+  await page.getByLabel('プロジェクト名').fill(unique('Proj'));
+  await page.getByRole('button', { name: '新規プロジェクト' }).click();
+  await expect(page).toHaveURL(/\/projects\/\d+$/);
+  return Number(page.url().match(/\/projects\/(\d+)/)![1]);
+}
+
+test.describe('activity log', () => {
+  test('board post and todo creation are recorded in the project activity log', async ({
+    page,
+  }) => {
+    const projectId = await setupOwner(page);
+
+    // 掲示板投稿 → board_posted アクティビティ
+    await page.request.post(`/api/projects/${projectId}/board/threads`, {
+      data: { title: unique('Thread'), bodyMd: 'body', category: 'notice' },
+    });
+    // ToDo作成 → todo_created アクティビティ
+    const cols = (
+      (await (
+        await page.request.get(`/api/projects/${projectId}/todos/columns`)
+      ).json()) as {
+        columns: { id: number }[];
+      }
+    ).columns;
+    await page.request.post(`/api/projects/${projectId}/todos/items`, {
+      data: { title: unique('Task'), columnId: cols[0].id },
+    });
+
+    // アクティビティ画面に両方のアクションが記録されている
+    await page.goto(`/projects/${projectId}/activity`);
+    await expect(page.getByText('掲示板投稿')).toBeVisible();
+    await expect(page.getByText('ToDo作成')).toBeVisible();
+  });
+});