feat: migrate Claude common config snippet from localStorage to config.json

Migrate the Claude common config snippet storage from browser localStorage
to the persistent config.json file for better cross-device sync and backup support.

**Backend Changes:**
- Add `claude_common_config_snippet` field to `MultiAppConfig` struct
- Add `get_claude_common_config_snippet` and `set_claude_common_config_snippet` Tauri commands
- Include JSON validation in the setter command

**Frontend Changes:**
- Create new `lib/api/config.ts` API module
- Refactor `useCommonConfigSnippet` hook to use config.json instead of localStorage
- Add automatic one-time migration from localStorage to config.json
- Add loading state during initialization

**Benefits:**
- Cross-device synchronization via backup/restore
- More reliable persistence than browser storage
- Centralized configuration management
- Seamless migration for existing users

src-tauri/src/app_config.rs

@@ -95,6 +95,9 @@ pub struct MultiAppConfig {
     /// Prompt 配置（按客户端分治）
     #[serde(default)]
     pub prompts: PromptRoot,
+    /// Claude 通用配置片段（JSON 字符串，用于跨供应商共享配置）
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub claude_common_config_snippet: Option<String>,
 }
 
 fn default_version() -> u32 {
@@ -113,6 +116,7 @@ impl Default for MultiAppConfig {
             apps,
             mcp: McpRoot::default(),
             prompts: PromptRoot::default(),
+            claude_common_config_snippet: None,
         }
     }
 }

src-tauri/src/commands/config.rs

@@ -135,3 +135,39 @@ pub async fn open_app_config_folder(handle: AppHandle) -> Result<bool, String> {
 
     Ok(true)
 }
+
+/// 获取 Claude 通用配置片段
+#[tauri::command]
+pub async fn get_claude_common_config_snippet(
+    state: tauri::State<'_, crate::store::AppState>,
+) -> Result<Option<String>, String> {
+    let guard = state.config.read().map_err(|e| format!("读取配置锁失败: {e}"))?;
+    Ok(guard.claude_common_config_snippet.clone())
+}
+
+/// 设置 Claude 通用配置片段
+#[tauri::command]
+pub async fn set_claude_common_config_snippet(
+    snippet: String,
+    state: tauri::State<'_, crate::store::AppState>,
+) -> Result<(), String> {
+    let mut guard = state
+        .config
+        .write()
+        .map_err(|e| format!("写入配置锁失败: {e}"))?;
+
+    // 验证是否为有效的 JSON（如果不为空）
+    if !snippet.trim().is_empty() {
+        serde_json::from_str::<serde_json::Value>(&snippet)
+            .map_err(|e| format!("无效的 JSON 格式: {e}"))?;
+    }
+
+    guard.claude_common_config_snippet = if snippet.trim().is_empty() {
+        None
+    } else {
+        Some(snippet)
+    };
+
+    guard.save().map_err(|e| e.to_string())?;
+    Ok(())
+}

src-tauri/src/lib.rs

@@ -511,6 +511,8 @@ pub fn run() {
             commands::get_init_error,
             commands::get_app_config_path,
             commands::open_app_config_folder,
+            commands::get_claude_common_config_snippet,
+            commands::set_claude_common_config_snippet,
             commands::read_live_provider_settings,
             commands::get_settings,
             commands::save_settings,