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.

main.go

@@ -0,0 +1,37 @@
+package main
+
+import (
+	"context"
+	"embed"
+	"log"
+
+	"github.com/wailsapp/wails/v2"
+	"github.com/wailsapp/wails/v2/pkg/options"
+	"github.com/wailsapp/wails/v2/pkg/options/assetserver"
+)
+
+//go:embed all:frontend/dist
+var assets embed.FS
+
+func main() {
+	as := NewAdminService()
+
+	err := wails.Run(&options.App{
+		Title:  "matrix_admin_panel",
+		Width:  1400,
+		Height: 880,
+		AssetServer: &assetserver.Options{
+			Assets: assets,
+		},
+		BackgroundColour: &options.RGBA{R: 26, G: 27, B: 30, A: 1},
+		OnStartup: func(ctx context.Context) {
+			as.SetContext(ctx)
+		},
+		Bind: []interface{}{
+			as,
+		},
+	})
+	if err != nil {
+		log.Fatalln("Wails error:", err)
+	}
+}