(auth): Add proxy authentication WebView for server login

lib/core/auth/native_cookie_manager.dart

@@ -0,0 +1,62 @@
+import 'package:flutter/foundation.dart';
+import 'package:flutter/services.dart';
+
+import '../utils/debug_logger.dart';
+
+/// Native cookie manager for accessing cookies from the platform's cookie store.
+///
+/// On iOS, this accesses WKHTTPCookieStore (shared with WKWebView).
+/// On Android, this accesses CookieManager (shared with WebView).
+///
+/// This is necessary because dart:io HttpClient has its own isolated cookie
+/// store that doesn't share with WebView.
+class NativeCookieManager {
+  static const _channel = MethodChannel('com.conduit.app/cookies');
+
+  /// Gets all cookies for a given URL from the native cookie store.
+  ///
+  /// Returns a map of cookie name -> value.
+  /// Returns empty map on web or if native method fails.
+  static Future<Map<String, String>> getCookiesForUrl(String url) async {
+    if (kIsWeb) return {};
+
+    try {
+      final result = await _channel.invokeMethod<Map<dynamic, dynamic>>(
+        'getCookies',
+        {'url': url},
+      );
+
+      if (result == null) return {};
+
+      final cookies = <String, String>{};
+      for (final entry in result.entries) {
+        cookies[entry.key.toString()] = entry.value.toString();
+      }
+
+      DebugLogger.auth('Retrieved ${cookies.length} cookies from native store');
+      return cookies;
+    } on MissingPluginException {
+      // Platform channels not implemented - fall back gracefully
+      DebugLogger.log(
+        'Native cookie manager not available on this platform',
+        scope: 'auth/cookies',
+      );
+      return {};
+    } catch (e) {
+      DebugLogger.warning(
+        'Failed to get native cookies',
+        scope: 'auth/cookies',
+        data: {'error': e.toString()},
+      );
+      return {};
+    }
+  }
+
+  /// Formats cookies as a Cookie header string.
+  static String formatCookieHeader(Map<String, String> cookies) {
+    if (cookies.isEmpty) return '';
+    return cookies.entries.map((e) => '${e.key}=${e.value}').join('; ');
+  }
+}
+
+