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

components/project/DeleteProjectButton.tsx

@@ -0,0 +1,51 @@
+'use client';
+
+import { useState } from 'react';
+import { useRouter } from 'next/navigation';
+
+export function DeleteProjectButton({ projectId }: { projectId: number }) {
+  const router = useRouter();
+  const [busy, setBusy] = useState(false);
+  const [error, setError] = useState<string | null>(null);
+
+  async function onDelete() {
+    if (
+      !window.confirm('プロジェクトを削除しますか？この操作は取り消せません。')
+    ) {
+      return;
+    }
+    setBusy(true);
+    setError(null);
+    const res = await fetch(`/api/projects/${projectId}`, {
+      method: 'DELETE',
+    });
+    setBusy(false);
+    if (res.ok) {
+      router.push('/dashboard');
+      router.refresh();
+    } else {
+      const body = (await res.json().catch(() => null)) as {
+        error?: { message?: string };
+      } | null;
+      setError(body?.error?.message ?? '削除に失敗しました');
+    }
+  }
+
+  return (
+    <div className="mt-3">
+      <button
+        type="button"
+        onClick={onDelete}
+        disabled={busy}
+        className="rounded bg-red-600 px-4 py-2 text-sm font-medium text-white hover:bg-red-700 disabled:opacity-50"
+      >
+        {busy ? '削除中...' : 'プロジェクトを削除'}
+      </button>
+      {error && (
+        <p className="mt-2 text-sm text-red-600" role="alert">
+          {error}
+        </p>
+      )}
+    </div>
+  );
+}