feat(m12): meetings + schedule conflict detection, tests, e2e

- MeetingRepository (CRUD, soft-delete, members, findMeetingsByUserInRange
  overlap) + CalendarRepository.findByCreatorInRange + TodoRepository.
  findHighPriorityByAssignee
- MeetingService (createMeeting tx+members, meeting_invited notify,
  meeting_created activity, SSE meeting.created; updateMeeting/updateMinutes/
  deleteMeeting; checkScheduleConflicts = other meetings overlap + calendar
  events overlap + high-priority todos due +-3d, time-overlap logic,
  excludeMeetingId; conflicts are warnings)
- APIs: meetings list/create/edit + /check conflict check
- Screens: meetings page + MeetingForm(member checkboxes, conflict display)
  + ConflictWarning, ProjectNav link
- Unit tests (MeetingRepository, MeetingService incl. conflict algorithm)
  + e2e meetings

tests/e2e/meetings.spec.ts

@@ -0,0 +1,77 @@
+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('meetings & schedule conflict', () => {
+  test('create meetings and detect a schedule conflict for a member', async ({
+    page,
+    request,
+  }) => {
+    const projectId = await setupOwner(page);
+    const memberEmail = unique('member') + '@example.com';
+
+    // メンバー登録してプロジェクトに追加
+    await request.post('/api/auth/register', {
+      data: { name: 'Member', email: memberEmail, password: 'password123' },
+    });
+    const addRes = await page.request.post(
+      `/api/projects/${projectId}/members`,
+      { data: { email: memberEmail, role: 'member' } }
+    );
+    const memberId = ((await addRes.json()) as { member: { userId: number } })
+      .member.userId;
+
+    // 1件目ミーティング(10:00-11:00)に member 参加
+    const m1 = await page.request.post(`/api/projects/${projectId}/meetings`, {
+      data: {
+        title: unique('M1'),
+        startAt: '2026-06-15T10:00:00',
+        endAt: '2026-06-15T11:00:00',
+        memberIds: [memberId],
+      },
+    });
+    expect(m1.ok()).toBeTruthy();
+    expect(((await m1.json()) as { conflicts: unknown[] }).conflicts).toEqual(
+      []
+    );
+
+    // 2件目(10:30-11:30)は member にとって重複 → 警告が返る
+    const m2 = await page.request.post(`/api/projects/${projectId}/meetings`, {
+      data: {
+        title: unique('M2'),
+        startAt: '2026-06-15T10:30:00',
+        endAt: '2026-06-15T11:30:00',
+        memberIds: [memberId],
+      },
+    });
+    expect(m2.ok()).toBeTruthy();
+    const m2Body = (await m2.json()) as {
+      meeting: { id: number };
+      conflicts: { type: string }[];
+    };
+    expect(m2Body.conflicts.some((c) => c.type === 'meeting')).toBe(true);
+
+    // ミーティング一覧画面に両方表示
+    await page.goto(`/projects/${projectId}/meetings`);
+    await expect(
+      page.getByTestId(`meeting-${m2Body.meeting.id}`)
+    ).toBeVisible();
+  });
+});