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/notifications.spec.ts

@@ -0,0 +1,69 @@
+import { test, expect, type Page } from '@playwright/test';
+
+function unique(prefix: string): string {
+  return `${prefix}-${Date.now()}-${Math.floor(Math.random() * 1_000_000)}`;
+}
+
+async function registerAndLogin(page: Page, email: string, name: string) {
+  await page.goto('/login');
+  await page.getByRole('button', { name: '新規登録はこちら' }).click();
+  await page.getByLabel('表示名').fill(name);
+  await page.getByLabel('メールアドレス').fill(email);
+  await page.getByLabel('パスワード').fill('password123');
+  await page.getByRole('button', { name: '登録する' }).click();
+  await expect(page).toHaveURL(/\/dashboard/);
+}
+
+test.describe('notifications', () => {
+  test('member-added notification appears and can be marked read', async ({
+    browser,
+  }) => {
+    const ownerEmail = unique('owner') + '@example.com';
+    const memberEmail = unique('member') + '@example.com';
+
+    // メンバーを先に登録(UIで作成+ログイン)
+    const memberContext = await browser.newContext();
+    const memberPage = await memberContext.newPage();
+    await registerAndLogin(memberPage, memberEmail, 'Member');
+
+    // オーナー登録＋プロジェクト作成
+    const ownerContext = await browser.newContext();
+    const ownerPage = await ownerContext.newPage();
+    await registerAndLogin(ownerPage, ownerEmail, 'Owner');
+    await ownerPage.getByLabel('プロジェクト名').fill(unique('Proj'));
+    await ownerPage.getByRole('button', { name: '新規プロジェクト' }).click();
+    await expect(ownerPage).toHaveURL(/\/projects\/\d+$/);
+    const projectId = Number(ownerPage.url().match(/\/projects\/(\d+)/)![1]);
+
+    // メンバー追加 → project_added 通知がメンバーへ
+    const addRes = await ownerPage.request.post(
+      `/api/projects/${projectId}/members`,
+      { data: { email: memberEmail, role: 'member' } }
+    );
+    expect(addRes.ok()).toBeTruthy();
+
+    // メンバーの通知一覧に表示
+    await memberPage.goto('/notifications');
+    await expect(
+      memberPage.getByText('プロジェクトに追加されました')
+    ).toBeVisible();
+
+    // 既読化(API) → 一覧が空になる
+    const listRes = await memberPage.request.get('/api/notifications?page=1');
+    const { items } = (await listRes.json()) as {
+      items: { id: number }[];
+    };
+    expect(items).toHaveLength(1);
+    const readRes = await memberPage.request.post(
+      `/api/notifications/${items[0].id}/read`
+    );
+    expect(readRes.ok()).toBeTruthy();
+    await memberPage.reload();
+    await expect(
+      memberPage.getByText('未読の通知はありません。')
+    ).toBeVisible();
+
+    await ownerContext.close();
+    await memberContext.close();
+  });
+});