feat(gemini): add config.json editor and common config functionality

Implements dual-editor pattern for Gemini providers, following the Codex architecture:
- Environment variables (.env format) editor
- Extended configuration (config.json) editor with common config support

New Components:
- GeminiConfigSections: Separate sections for env and config editing
- GeminiCommonConfigModal: Modal for editing common config snippets

New Hooks:
- useGeminiConfigState: Manages env/config separation and conversion
  - Converts between .env string format and JSON object
  - Validates JSON config structure
  - Extracts API Key and Base URL from env
- useGeminiCommonConfig: Handles common config snippets
  - Deep merge algorithm for combining configs
  - Remove common config logic for toggling off
  - localStorage persistence for snippets

Features:
- Format buttons for both env and config editors
- Common config toggle with deep merge/remove
- Error validation and display
- Auto-open modal on common config errors

Configuration Structure:
{
  "env": {
    "GOOGLE_GEMINI_BASE_URL": "https://...",
    "GEMINI_API_KEY": "sk-...",
    "GEMINI_MODEL": "gemini-2.5-pro"
  },
  "config": {
    "timeout": 30000,
    "maxRetries": 3
  }
}

This brings Gemini providers to feature parity with Claude and Codex.

src/components/providers/forms/hooks/useCommonConfigSnippet.ts

@@ -29,8 +29,9 @@ export function useCommonConfigSnippet({
   initialData,
 }: UseCommonConfigSnippetProps) {
   const [useCommonConfig, setUseCommonConfig] = useState(false);
-  const [commonConfigSnippet, setCommonConfigSnippetState] =
-    useState<string>(DEFAULT_COMMON_CONFIG_SNIPPET);
+  const [commonConfigSnippet, setCommonConfigSnippetState] = useState<string>(
+    DEFAULT_COMMON_CONFIG_SNIPPET,
+  );
   const [commonConfigError, setCommonConfigError] = useState("");
   const [isLoading, setIsLoading] = useState(true);
 
@@ -64,7 +65,9 @@ export function useCommonConfigSnippet({
                 }
                 // 清理 localStorage
                 window.localStorage.removeItem(LEGACY_STORAGE_KEY);
-                console.log("[迁移] 通用配置已从 localStorage 迁移到 config.json");
+                console.log(
+                  "[迁移] 通用配置已从 localStorage 迁移到 config.json",
+                );
               }
             } catch (e) {
               console.warn("[迁移] 从 localStorage 迁移失败:", e);