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

components/layout/ProjectNav.tsx

@@ -7,6 +7,7 @@ const NAV_ITEMS = [
   { href: '/files', label: 'ファイル' },
   { href: '/calendar', label: 'カレンダー' },
   { href: '/milestones', label: 'マイルストーン' },
+  { href: '/meetings', label: 'ミーティング' },
   { href: '/members', label: 'メンバー' },
   { href: '/activity', label: 'アクティビティ' },
   { href: '/settings', label: '設定' },
@@ -30,6 +31,7 @@ export function ProjectNav({
     | 'files'
     | 'calendar'
     | 'milestones'
+    | 'meetings'
     | 'members'
     | 'activity'
     | 'settings';
@@ -43,6 +45,7 @@ export function ProjectNav({
     files: active === 'files',
     calendar: active === 'calendar',
     milestones: active === 'milestones',
+    meetings: active === 'meetings',
     members: active === 'members',
     activity: active === 'activity',
     settings: active === 'settings',

components/meetings/ConflictWarning.tsx

@@ -0,0 +1,46 @@
+export interface ScheduleConflict {
+  userId: number;
+  type: 'meeting' | 'calendar_event' | 'important_todo';
+  refId: number;
+  title: string;
+  startAt: string;
+  endAt: string | null;
+}
+
+const TYPE_LABELS: Record<string, string> = {
+  meeting: 'ミーティング',
+  calendar_event: 'カレンダーイベント',
+  important_todo: '期限の近い重要タスク',
+};
+
+export function ConflictWarning({
+  conflicts,
+}: {
+  conflicts: ScheduleConflict[];
+}) {
+  if (conflicts.length === 0) {
+    return (
+      <p className="text-sm text-green-600" data-testid="no-conflicts">
+        スケジュールの重複はありません。
+      </p>
+    );
+  }
+  return (
+    <div
+      className="rounded border border-yellow-300 bg-yellow-50 p-3"
+      data-testid="conflict-warning"
+    >
+      <p className="text-sm font-semibold text-yellow-800">
+        スケジュールの重複があります（作成は完了しています）:
+      </p>
+      <ul className="mt-1 list-inside list-disc text-sm text-yellow-800">
+        {conflicts.map((c, i) => (
+          <li key={i}>
+            [{TYPE_LABELS[c.type] ?? c.type}] {c.title}（{c.startAt}
+            {c.endAt ? ` 〜 ${c.endAt}` : ''}）
+          </li>
+        ))}
+      </ul>
+    </div>
+  );
+}

components/meetings/MeetingForm.tsx

@@ -0,0 +1,143 @@
+'use client';
+
+import { useState, type FormEvent } from 'react';
+import { useRouter } from 'next/navigation';
+import {
+  ConflictWarning,
+  type ScheduleConflict,
+} from '@/components/meetings/ConflictWarning';
+
+interface Member {
+  userId: number;
+  name: string;
+}
+
+export function MeetingForm({
+  projectId,
+  members,
+}: {
+  projectId: number;
+  members: Member[];
+}) {
+  const router = useRouter();
+  const [title, setTitle] = useState('');
+  const [startAt, setStartAt] = useState('');
+  const [endAt, setEndAt] = useState('');
+  const [selected, setSelected] = useState<number[]>([]);
+  const [conflicts, setConflicts] = useState<ScheduleConflict[] | null>(null);
+  const [loading, setLoading] = useState(false);
+  const [error, setError] = useState<string | null>(null);
+
+  async function onSubmit(event: FormEvent<HTMLFormElement>) {
+    event.preventDefault();
+    setLoading(true);
+    setError(null);
+    setConflicts(null);
+    const res = await fetch(`/api/projects/${projectId}/meetings`, {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({ title, startAt, endAt, memberIds: selected }),
+    });
+    setLoading(false);
+    if (res.ok) {
+      const data = (await res.json()) as {
+        meeting: { id: number };
+        conflicts: ScheduleConflict[];
+      };
+      setConflicts(data.conflicts);
+      setTitle('');
+      setStartAt('');
+      setEndAt('');
+      setSelected([]);
+      router.refresh();
+    } else {
+      const b = (await res.json().catch(() => null)) as {
+        error?: { message?: string };
+      } | null;
+      setError(b?.error?.message ?? '作成に失敗しました');
+    }
+  }
+
+  function toggleMember(userId: number) {
+    setSelected((prev) =>
+      prev.includes(userId)
+        ? prev.filter((u) => u !== userId)
+        : [...prev, userId]
+    );
+  }
+
+  return (
+    <form
+      onSubmit={onSubmit}
+      className="space-y-3 rounded-lg border bg-white p-4 shadow-sm"
+      data-testid="meeting-form"
+    >
+      <div>
+        <label className="block text-sm font-medium">タイトル</label>
+        <input
+          type="text"
+          value={title}
+          onChange={(e) => setTitle(e.target.value)}
+          className="mt-1 w-full rounded border px-3 py-2"
+          required
+          data-testid="meeting-title"
+        />
+      </div>
+      <div className="flex gap-2">
+        <div className="flex-1">
+          <label className="block text-sm font-medium">開始</label>
+          <input
+            type="datetime-local"
+            value={startAt}
+            onChange={(e) => setStartAt(e.target.value)}
+            className="mt-1 w-full rounded border px-3 py-2"
+            required
+            data-testid="meeting-start"
+          />
+        </div>
+        <div className="flex-1">
+          <label className="block text-sm font-medium">終了</label>
+          <input
+            type="datetime-local"
+            value={endAt}
+            onChange={(e) => setEndAt(e.target.value)}
+            className="mt-1 w-full rounded border px-3 py-2"
+            required
+            data-testid="meeting-end"
+          />
+        </div>
+      </div>
+      <div>
+        <label className="block text-sm font-medium">参加メンバー</label>
+        <div className="mt-1 flex flex-wrap gap-2">
+          {members.map((m) => (
+            <label
+              key={m.userId}
+              className="flex items-center gap-1 rounded border px-2 py-1 text-sm"
+            >
+              <input
+                type="checkbox"
+                checked={selected.includes(m.userId)}
+                onChange={() => toggleMember(m.userId)}
+              />
+              {m.name}
+            </label>
+          ))}
+        </div>
+      </div>
+      {error && (
+        <p className="text-sm text-red-600" role="alert">
+          {error}
+        </p>
+      )}
+      <button
+        type="submit"
+        disabled={loading}
+        className="rounded bg-blue-600 px-4 py-2 font-medium text-white hover:bg-blue-700 disabled:opacity-50"
+      >
+        {loading ? '作成中...' : 'ミーティング作成'}
+      </button>
+      {conflicts && <ConflictWarning conflicts={conflicts} />}
+    </form>
+  );
+}