feat: add CLI settings export/import functionality

- Implemented exportSettings and importSettings APIs for CLI settings.
- Added hooks useExportSettings and useImportSettings for managing export/import operations in the frontend.
- Updated SettingsPage to include buttons for exporting and importing CLI settings.
- Enhanced backend to handle export and import requests, including validation and conflict resolution.
- Introduced new data structures for exported settings and import options.
- Updated localization files to support new export/import features.
- Refactored CLI tool configurations to remove hardcoded model defaults, allowing dynamic model retrieval.

ccw/src/tools/cli-executor-core.ts

@@ -958,12 +958,16 @@ async function executeCliTool(
 
     // Merge custom env with process.env (custom env takes precedence)
     // Also include rulesEnv for $PROTO and $TMPL template variables
-    const spawnEnv = {
+    const spawnEnv: Record<string, string | undefined> = {
       ...process.env,
       ...customEnv,
       ...(rulesEnv || {})
     };
 
+    // Unset CLAUDECODE to allow nested Claude Code sessions (SDK/subagent use case)
+    // See: https://github.com/anthropics/claude-agent-sdk-python/issues/573
+    delete spawnEnv.CLAUDECODE;
+
     debugLog('SPAWN', `Spawning process`, {
       command,
       args,