fix: v2.0.4+24 — login fixes, signup toggle, forgot-password, guest SnackBar, Google OAuth

- Google Sign-In: wire serverClientId (639347358523-mtkm...apps.googleusercontent.com) so idToken is returned on Android
- Email login: raise timeout 10s→25s, add single retry on SocketException/TimeoutException
- Forgot Password: real glassmorphism bottom sheet with safe-degrade SnackBar (endpoint missing on backend)
- Create Account: same-page AnimatedSwitcher toggle with glassmorphism signup form; delete old RegisterScreen
- Desktop parity: DesktopLoginScreen same-page toggle; delete DesktopRegisterScreen
- Guest mode: remove ScaffoldMessenger SnackBar from HomeScreen outer catch (inner _safe wrappers already return [])
- LoginScreen: clearSnackBars() on postFrameCallback to prevent carried-over SnackBars from prior screens
- ProGuard: add Google Sign-In + OkHttp keep rules
- Version bump: 2.0.0+20 → 2.0.4+24; settings _appVersion → 2.0.4

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

lib/core/api/api_client.dart

@@ -1,12 +1,15 @@
 // lib/core/api/api_client.dart
+import 'dart:async';
 import 'dart:convert';
+import 'dart:io' show SocketException;
 import 'package:flutter/foundation.dart';
 import 'package:http/http.dart' as http;
 import 'package:http_parser/http_parser.dart';
 import '../storage/token_storage.dart';
 
 class ApiClient {
-  static const Duration _timeout = Duration(seconds: 10);
+  static const Duration _timeout = Duration(seconds: 25);
+  static const Duration _retryDelay = Duration(milliseconds: 600);
   // Set to true to enable mock/offline development mode (useful when backend is unavailable)
   static const bool _developmentMode = false;
 
@@ -28,13 +31,7 @@ class ApiClient {
 
     late http.Response response;
     try {
-      response = await http
-          .post(
-            Uri.parse(url),
-            headers: headers,
-            body: jsonEncode(finalBody),
-          )
-          .timeout(_timeout);
+      response = await _postWithRetry(url, headers, finalBody);
     } catch (e) {
       if (kDebugMode) debugPrint('ApiClient.post network error: $e');
 
@@ -100,6 +97,32 @@ class ApiClient {
     return _handleResponse(url, response, finalBody);
   }
 
+  /// POST with one retry on transient network errors.
+  /// Retries on SocketException / TimeoutException only.
+  Future<http.Response> _postWithRetry(
+    String url,
+    Map<String, String> headers,
+    Map<String, dynamic> body,
+  ) async {
+    try {
+      return await http
+          .post(Uri.parse(url), headers: headers, body: jsonEncode(body))
+          .timeout(_timeout);
+    } on SocketException {
+      if (kDebugMode) debugPrint('ApiClient.post retry after SocketException');
+      await Future.delayed(_retryDelay);
+      return await http
+          .post(Uri.parse(url), headers: headers, body: jsonEncode(body))
+          .timeout(_timeout);
+    } on TimeoutException {
+      if (kDebugMode) debugPrint('ApiClient.post retry after TimeoutException');
+      await Future.delayed(_retryDelay);
+      return await http
+          .post(Uri.parse(url), headers: headers, body: jsonEncode(body))
+          .timeout(_timeout);
+    }
+  }
+
   /// Upload a single file as multipart/form-data.
   ///
   /// Returns the `file` object from the server response: