refactor(common-config): consolidate hooks and migrate Gemini to ENV format

- Delete redundant wrapper hooks (useCommonConfigSnippet, useGeminiCommonConfig)
- Change Gemini common config from JSON to ENV format (.env style)
- Add backend validation with forbidden keys filtering (GEMINI_API_KEY, GOOGLE_GEMINI_BASE_URL)
- Fix localStorage migration to skip empty parsed snippets
- Add error handling for silent JSON parse failures
- Clean up debug logs and unused types

src/hooks/commonConfigAdapters.ts

@@ -249,7 +249,7 @@ export const codexAdapter: CommonConfigAdapter<string, string> = {
 // ============================================================================
 
 const GEMINI_LEGACY_STORAGE_KEY = "cc-switch:gemini-common-config-snippet";
-const GEMINI_DEFAULT_SNIPPET = "{}";
+const GEMINI_DEFAULT_SNIPPET = "";
 
 export interface GeminiAdapterOptions {
   /** 字符串转对象 */
@@ -306,7 +306,9 @@ export function createGeminiAdapter(
         ) {
           return t("geminiConfig.commonConfigInvalidValues");
         }
-        return t("geminiConfig.invalidJsonFormat");
+        return t("geminiConfig.invalidEnvFormat", {
+          defaultValue: "配置格式错误",
+        });
       }
 
       if (Object.keys(result.env).length === 0) {

src/hooks/useCommonConfigBase.ts

@@ -234,7 +234,9 @@ export function useCommonConfigBase<TConfig, TFinal>({
             );
             if (legacySnippet && legacySnippet.trim()) {
               const parsed = adapter.parseSnippet(legacySnippet);
-              if (!parsed.error) {
+              // 只有在解析成功且有有效内容时才迁移
+              // 这避免了将 "{}" 这样的空 JSON 迁移为"有效配置"
+              if (!parsed.error && adapter.hasValidContent(legacySnippet)) {
                 await configApi.setCommonConfigSnippet(
                   adapter.appKey,
                   legacySnippet,
@@ -246,6 +248,9 @@ export function useCommonConfigBase<TConfig, TFinal>({
                 console.log(
                   `[迁移] ${adapter.appKey} 通用配置已从 localStorage 迁移到数据库`,
                 );
+              } else {
+                // 解析失败或无有效内容，清理 localStorage 不迁移
+                window.localStorage.removeItem(adapter.legacyStorageKey);
               }
             }
           } catch (e) {