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

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

@@ -0,0 +1,58 @@
+import { NextRequest, NextResponse } from 'next/server';
+import { getCurrentUser } from '@/lib/auth/getCurrentUser';
+import { createMeetingService } from '@/lib/api/services';
+import { UnauthorizedError } from '@/lib/errors';
+import { handleApiError, jsonError } from '@/lib/api/handleError';
+
+export const runtime = 'nodejs';
+
+export async function GET(
+  _request: NextRequest,
+  { params }: { params: Promise<{ projectId: string }> }
+) {
+  const user = await getCurrentUser();
+  if (!user) return handleApiError(new UnauthorizedError());
+  const { projectId } = await params;
+  const service = createMeetingService();
+  try {
+    return NextResponse.json({
+      meetings: service.getMeetings(user.id, Number(projectId)),
+    });
+  } catch (error) {
+    return handleApiError(error);
+  }
+}
+
+export async function POST(
+  request: NextRequest,
+  { params }: { params: Promise<{ projectId: string }> }
+) {
+  const user = await getCurrentUser();
+  if (!user) return handleApiError(new UnauthorizedError());
+  const { projectId } = await params;
+  let body: Record<string, unknown>;
+  try {
+    body = (await request.json()) as Record<string, unknown>;
+  } catch {
+    return jsonError(400, 'リクエスト本文が不正です');
+  }
+  const service = createMeetingService();
+  try {
+    const result = service.createMeeting(user.id, Number(projectId), {
+      title: String(body.title ?? ''),
+      startAt: String(body.startAt ?? ''),
+      endAt: String(body.endAt ?? ''),
+      description:
+        typeof body.description === 'string' ? body.description : null,
+      location: typeof body.location === 'string' ? body.location : null,
+      meetingUrl: typeof body.meetingUrl === 'string' ? body.meetingUrl : null,
+      agendaMd: typeof body.agendaMd === 'string' ? body.agendaMd : null,
+      memberIds: Array.isArray(body.memberIds)
+        ? body.memberIds.map(Number)
+        : [],
+    });
+    return NextResponse.json(result, { status: 201 });
+  } catch (error) {
+    return handleApiError(error);
+  }
+}