feat: Add --to-file option to ccw cli for saving output to files

Adds support for saving CLI execution output directly to files with the following features:
- Support for relative paths: --to-file output.txt
- Support for nested directories: --to-file results/analysis/output.txt (auto-creates directories)
- Support for absolute paths: --to-file /tmp/output.txt or --to-file D:/results/output.txt
- Works in both streaming and non-streaming modes
- Automatically creates parent directories if they don't exist
- Proper error handling with user-friendly messages
- Shows file save location in completion feedback

Implementation details:
- Updated CLI option parser in ccw/src/cli.ts
- Added toFile parameter to CliExecOptions interface
- Implemented file saving logic in execAction() for both streaming and non-streaming modes
- Updated HTTP API endpoint /api/cli/execute to support toFile parameter
- All changes are backward compatible

Testing:
- Tested with relative paths (single and nested directories)
- Tested with absolute paths (Windows and Unix style)
- Tested with streaming mode
- All tests passed successfully

ccw/src/cli.ts

@@ -209,6 +209,7 @@ export function run(argv: string[]): void {
     .option('--turn <n>', 'Turn number for cache (default: latest)')
     .option('--raw', 'Raw output only (no formatting)')
     .option('--final', 'Output final result only with usage hint')
+    .option('--to-file <path>', 'Save output to file')
     .action((subcommand, args, options) => cliCommand(subcommand, args, options));
 
   // Memory command