fix: return native path from getDefaultBgOutputDir

The bgOutputDir is used by Node.js fs APIs (mkdir, writeFile) which need
native Windows paths. POSIX conversion happens at shell command construction
time via toPosixPath() in spawnBackground.

Author: ethanndickson

src/node/runtime/WorktreeRuntime.ts

@@ -287,7 +287,9 @@ export class WorktreeRuntime extends LocalBaseRuntime {
 
           // Force delete the directory (use bash shell for rm -rf on Windows)
           // Convert to POSIX path for Git Bash compatibility on Windows
-          using rmProc = execAsync(`rm -rf "${toPosixPath(deletedPath)}"`, { shell: getBashPath() });
+          using rmProc = execAsync(`rm -rf "${toPosixPath(deletedPath)}"`, {
+            shell: getBashPath(),
+          });
           await rmProc.result;
 
           return { success: true, deletedPath };