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/layout/Sidebar.tsx

@@ -0,0 +1,9 @@
+/**
+ * プロジェクトページ共通のサイドバー。
+ * プロジェクト内ナビゲーションは ProjectNav に委譲する。
+ */
+export function Sidebar({ children }: { children: React.ReactNode }) {
+  return (
+    <aside className="w-48 shrink-0 border-r bg-gray-50 p-4">{children}</aside>
+  );
+}