feat(m4): project & member management with tests and e2e

- ProjectRepository, ProjectMemberRepository, minimal NotificationRepository
- ProjectService: create/update/archive/delete project, add/remove member,
  permission checks (isMember/admin), member-added notification, getDashboard
  skeleton, getMyProjects, getMemberRole
- projectValidator, API services factory
- API routes: projects CRUD, members list/add/remove
- Screens: dashboard (project list + create form), project overview, members,
  settings; layout (Header/Sidebar/ProjectNav) and project components
- Unit tests (Project/ProjectMember repositories, ProjectService),
  integration project-member-permission, e2e project-management

app/projects/[projectId]/page.tsx

@@ -0,0 +1,79 @@
+import { redirect } from 'next/navigation';
+import { getCurrentUser, toPublicUser } from '@/lib/auth/getCurrentUser';
+import { createProjectService } from '@/lib/api/services';
+import { Header } from '@/components/layout/Header';
+import { ProjectNav } from '@/components/layout/ProjectNav';
+import { DashboardWidget } from '@/components/project/DashboardWidget';
+import { ForbiddenError, NotFoundError } from '@/lib/errors';
+
+export const dynamic = 'force-dynamic';
+
+const STATUS_LABELS: Record<string, string> = {
+  active: 'Active',
+  on_hold: 'On Hold',
+  completed: 'Completed',
+  archived: 'Archived',
+};
+
+export default async function ProjectOverviewPage({
+  params,
+}: {
+  params: Promise<{ projectId: string }>;
+}) {
+  const user = await getCurrentUser();
+  if (!user) {
+    redirect('/login');
+  }
+  const { projectId } = await params;
+
+  const service = createProjectService();
+  let dashboard;
+  try {
+    dashboard = service.getDashboard(user.id, Number(projectId));
+  } catch (error) {
+    if (error instanceof ForbiddenError || error instanceof NotFoundError) {
+      redirect('/dashboard');
+    }
+    throw error;
+  }
+
+  const { project, members } = dashboard;
+
+  return (
+    <div className="min-h-screen bg-gray-50">
+      <Header user={toPublicUser(user)} />
+      <ProjectNav projectId={project.id} active="overview" />
+      <main className="mx-auto max-w-4xl space-y-6 p-6">
+        <div className="flex items-center justify-between">
+          <h1 className="text-2xl font-bold">{project.name}</h1>
+          <span className="rounded bg-gray-100 px-2 py-0.5 text-xs">
+            {STATUS_LABELS[project.status] ?? project.status}
+          </span>
+        </div>
+        {project.description && (
+          <p className="text-gray-600">{project.description}</p>
+        )}
+        <p className="text-sm text-gray-500">メンバー数: {members.length}</p>
+
+        <div className="grid gap-4 sm:grid-cols-2">
+          <DashboardWidget
+            title="進行中ToDo"
+            empty="ToDo機能は後続マイルストーンで実装されます"
+          />
+          <DashboardWidget
+            title="最新チャット"
+            empty="チャット機能は後続マイルストーンで実装されます"
+          />
+          <DashboardWidget
+            title="最新掲示板"
+            empty="掲示板機能は後続マイルストーンで実装されます"
+          />
+          <DashboardWidget
+            title="最近のアクティビティ"
+            empty="アクティビティログは後続マイルストーンで実装されます"
+          />
+        </div>
+      </main>
+    </div>
+  );
+}