refactor(startup): improve first-launch import logic with per-table detection

- Replace global `is_empty_for_first_import()` with independent checks:
  - `is_mcp_table_empty()` for MCP server imports
  - `is_prompts_table_empty()` for prompt imports
  - Skills and providers already have built-in idempotency checks

- Fix misleading logs in provider import:
  - Change `import_default_config` return type from `Result<()>` to `Result<bool>`
  - Return `true` when actually imported, `false` when skipped
  - Only log success message when import actually occurred

- Add idempotency protection to `import_from_file_on_first_launch`

This allows each data type to be independently recovered if deleted,
rather than requiring all tables to be empty for any import to trigger.

src-tauri/src/services/prompt.rs

@@ -176,6 +176,12 @@ impl PromptService {
         state: &AppState,
         app: AppType,
     ) -> Result<usize, AppError> {
+        // 幂等性保护：该应用已有提示词则跳过
+        let existing = state.db.get_prompts(app.as_str())?;
+        if !existing.is_empty() {
+            return Ok(0);
+        }
+
         let file_path = prompt_file_path(&app)?;
 
         // 检查文件是否存在

src-tauri/src/services/provider/live.rs

@@ -215,11 +215,14 @@ pub fn read_live_settings(app_type: AppType) -> Result<Value, AppError> {
 }
 
 /// Import default configuration from live files
-pub fn import_default_config(state: &AppState, app_type: AppType) -> Result<(), AppError> {
+///
+/// Returns `Ok(true)` if a provider was actually imported,
+/// `Ok(false)` if skipped (providers already exist for this app).
+pub fn import_default_config(state: &AppState, app_type: AppType) -> Result<bool, AppError> {
     {
         let providers = state.db.get_all_providers(app_type.as_str())?;
         if !providers.is_empty() {
-            return Ok(());
+            return Ok(false); // 已有供应商，跳过
         }
     }
 
@@ -298,7 +301,7 @@ pub fn import_default_config(state: &AppState, app_type: AppType) -> Result<(),
         .db
         .set_current_provider(app_type.as_str(), &provider.id)?;
 
-    Ok(())
+    Ok(true) // 真正导入了
 }
 
 /// Write Gemini live configuration with authentication handling

src-tauri/src/services/provider/mod.rs

@@ -225,7 +225,9 @@ impl ProviderService {
     }
 
     /// Import default configuration from live files (re-export)
-    pub fn import_default_config(state: &AppState, app_type: AppType) -> Result<(), AppError> {
+    ///
+    /// Returns `Ok(true)` if imported, `Ok(false)` if skipped.
+    pub fn import_default_config(state: &AppState, app_type: AppType) -> Result<bool, AppError> {
         import_default_config(state, app_type)
     }