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.

README.md

@@ -0,0 +1,20 @@
+# matrix_admin_panel
+
+Panel admin Matrix propio. Sustituye `synapse-admin` (eliminado en issue 0162).
+
+Stack: Wails (Go) + React + Mantine v7. Login MAS OIDC PKCE (loopback :8766) + Synapse Admin API.
+
+## Dev
+
+```bash
+wails dev
+```
+
+## Build
+
+```bash
+wails build                                  # linux/amd64
+wails build -platform windows/amd64          # windows
+```
+
+Binary en `build/bin/matrix_admin_panel(.exe)`.