fix: 4 audit findings in professionals location flow

- Clear button (✕) now resets _cityMismatch and _detectedCity so banner and CTA unblock
- _citiesMatch: replace bidirectional contains with equality + word-prefix check to prevent 'Cali' matching 'Calima'
- ProfessionalsProvider: track _currentUserId to reset state on user change (cross-user leak)
- ProfessionalsProvider: store _lastSearch so setLocationContext preserves active search term

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

lib/main.dart

@@ -50,7 +50,7 @@ class AppState extends StatelessWidget {
         ChangeNotifierProvider(create: (_) => ProfessionalFormProvider()),
         ChangeNotifierProxyProvider<AuthProvider, ProfessionalsProvider>(
           create: (_) => ProfessionalsProvider(),
-          update: (_, auth, prev) => prev!..updateCity(auth.user?.city),
+          update: (_, auth, prev) => prev!..updateCity(auth.user?.city, userId: auth.user?.id),
         ),
         ChangeNotifierProvider(create: (_) => ServicesProvider()),
         ChangeNotifierProvider(create: (_) => CalendarServicesProvider()),