feat: implement full admin panel with dashboard, user management, and platform settings

Adds complete super_admin panel with 9 pages and account owner categories page.
Backend includes 5 new DB tables, ~25 API endpoints, settings manager with
in-memory cache, and 29 integration tests. Frontend includes reusable admin
components (DataTable, Pagination, ActionMenu, etc.) with code-split lazy loading.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/tests/test_admin_dashboard.py

@@ -0,0 +1,35 @@
+"""Integration tests for admin dashboard endpoints."""
+
+import pytest
+from httpx import AsyncClient
+
+
+class TestAdminDashboard:
+
+    @pytest.mark.asyncio
+    async def test_get_dashboard_metrics(
+        self, client: AsyncClient, admin_auth_headers: dict, test_user: dict
+    ):
+        """Super admin can get dashboard metrics."""
+        response = await client.get("/api/v1/admin/dashboard/metrics", headers=admin_auth_headers)
+        assert response.status_code == 200
+        data = response.json()
+        assert "total_users" in data
+        assert data["total_users"] >= 2  # admin + test_user
+
+    @pytest.mark.asyncio
+    async def test_get_dashboard_activity(
+        self, client: AsyncClient, admin_auth_headers: dict
+    ):
+        """Super admin can get recent activity."""
+        response = await client.get("/api/v1/admin/dashboard/activity", headers=admin_auth_headers)
+        assert response.status_code == 200
+        assert isinstance(response.json(), list)
+
+    @pytest.mark.asyncio
+    async def test_non_admin_cannot_access_dashboard(
+        self, client: AsyncClient, auth_headers: dict
+    ):
+        """Non-admin gets 403."""
+        response = await client.get("/api/v1/admin/dashboard/metrics", headers=auth_headers)
+        assert response.status_code == 403