feat(auth): implement dual-flow authentication (web + mobile)

Add complete authentication system supporting both web (NPM forward auth)
and mobile (OIDC) authentication flows.

Web flow:
- Check /auth/me on startup to detect NPM forward auth session
- Cookies handled by proxy, no Bearer tokens needed

Mobile flow:
- flutter_appauth for OIDC Authorization Code + PKCE
- POST /auth/sync to get user profile and roles
- Token storage in SharedPreferences

Shared:
- Permission system with Domain/Action enums and Role class
- PermissionGate and AdminGate widgets for UI permission checks
- Route guards redirecting unauthenticated users to login
- Login page with platform-specific messaging

Platform config:
- iOS: CFBundleURLTypes for net.schweitz.tatlock://
- Android: appAuthRedirectScheme, minSdk 23

Docs:
- Added Freezed 3.x sealed class documentation

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

lib/core/api/api_interceptors.dart

@@ -9,7 +9,9 @@ import 'package:tatlock_ui/core/error/app_exception.dart';
 
 /// Adds authentication token to requests.
 ///
-/// Skipped entirely when [AppConfig.requiresAuth] is false (LAN development).
+/// - **LAN mode**: Skipped entirely (no auth required)
+/// - **Web**: Skipped (cookies handle auth via NPM forward auth)
+/// - **Mobile**: Adds Bearer token from OIDC authentication
 class AuthInterceptor extends Interceptor {
   AuthInterceptor(this._ref);
 
@@ -23,10 +25,17 @@ class AuthInterceptor extends Interceptor {
       return;
     }
 
+    // Skip Bearer token on web - cookies handle auth via NPM forward auth
+    if (kIsWeb) {
+      handler.next(options);
+      return;
+    }
+
+    // Mobile: Add Bearer token from OIDC authentication
     final authState = _ref.read(authProvider);
 
     authState.whenData((auth) {
-      if (auth.isAuthenticated && auth.accessToken != null) {
+      if (auth.isAuthenticated && auth.accessToken != null && auth.accessToken != 'web-session') {
         options.headers['Authorization'] = 'Bearer ${auth.accessToken}';
       }
     });