feat: scaffold matrix_admin_panel v0.1.0 (issue 0163)

Wails + React + Mantine v7 admin panel for Matrix/Synapse. Replaces the
removed synapse-admin container. MAS OIDC PKCE login (loopback :8766) +
Synapse Admin API (users/rooms/sessions).

- MAS client: XSFD2SWA394DXRVJFTREAMY6J6 (public PKCE, no auth method).
- Backend: AdminService (Go) with Login/SetAdminToken/ListUsers/
  DeactivateUser/ResetUserPassword/ListRooms/DeleteRoom/GetUserDevices.
- Vendored helpers in internal/infra/ from registry:
  mas_oidc_loopback_go_infra, keyring_token_store_go_infra,
  synapse_admin_client_go_infra.
- Frontend: AppShell + sidebar tabs (Users/Rooms/Sessions). Sessions
  placeholder pending MAS admin API.
- Build verified: Linux + Windows.

frontend/package.json

@@ -0,0 +1,26 @@
+{
+  "name": "matrix_admin_panel-frontend",
+  "private": true,
+  "version": "0.1.0",
+  "type": "module",
+  "scripts": {
+    "dev": "vite",
+    "build": "tsc && vite build",
+    "preview": "vite preview"
+  },
+  "dependencies": {
+    "@mantine/core": "^7.13.0",
+    "@mantine/hooks": "^7.13.0",
+    "@mantine/notifications": "^7.13.0",
+    "@tabler/icons-react": "^3.19.0",
+    "react": "^18.3.1",
+    "react-dom": "^18.3.1"
+  },
+  "devDependencies": {
+    "@types/react": "^18.3.10",
+    "@types/react-dom": "^18.3.0",
+    "@vitejs/plugin-react": "^4.3.1",
+    "typescript": "^5.6.2",
+    "vite": "^5.4.8"
+  }
+}