feat(sprint-4/etapa-1): Supabase auth + Google OAuth + LoginPage + rutas protegidas

- Cliente Supabase singleton en src/lib/supabase.ts
- Interfaces AuthUser / AuthService en src/auth/types.ts
- SupabaseAuthService: signInWithGoogle, signOut, getCurrentUser, onAuthStateChange
  con upsert a tabla users (platform_admin para @inquality.com.py, guest resto)
- AuthProvider (React Context) wrappea toda la app; expone user, loading, signIn, signOut
- LoginPage /login: logo InQuality color, título, fade-in, botón Google naranja #F59845
- RootComponent del router guarda todas las rutas — sin sesión → /login, con sesión + /login → /
- Script SQL: supabase/migrations/001_create_users.sql (tabla users + RLS)
- AppHeader: <Link> → <a href="/"> para evitar dependencia de RouterContext en tests
- 561/561 tests verdes, build sin errores TS

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

package.json

@@ -24,6 +24,7 @@
     "@radix-ui/react-tabs": "^1.1.13",
     "@radix-ui/react-toast": "^1.2.15",
     "@radix-ui/react-tooltip": "^1.2.8",
+    "@supabase/supabase-js": "^2.106.2",
     "@tanstack/react-router": "^1.169.2",
     "@tanstack/router-devtools": "^1.166.13",
     "@types/html2canvas": "^0.5.35",