feat(web): switch to path-based URL strategy

Remove hash from URLs (/#/login -> /login) using usePathUrlStrategy().
Uses conditional imports to only apply on web, keeping mobile/desktop
builds unaffected.

Required for OIDC callback to work - Authentik redirects to /callback
which Flutter now recognizes as a route.

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

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

lib/main.dart

@@ -4,11 +4,15 @@ import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 
 import 'app.dart';
+import 'core/config/url_strategy.dart';
 import 'version.g.dart';
 
 void main() {
   WidgetsFlutterBinding.ensureInitialized();
 
+  // Use path-based URLs on web (no-op on mobile/desktop)
+  configureUrlStrategy();
+
   developer.log(
     '${AppVersion.name} v${AppVersion.fullVersion}',
     name: 'tatlock_ui',