fix(electrobun): PathBrowser uses unguarded files.browse RPC (dirs only)

- files.browse: new RPC handler — unguarded directory listing, returns
  only directories (no file content access). Used by PathBrowser wizard.
- PathBrowser: uses files.browse instead of files.list (was blocked by
  guardPath "access denied: path outside allowed project directories")
- Home dir resolved via files.homeDir RPC (not process.env.HOME)

Note: GTK native dialog title/theme/sort controlled by Electrobun's
native wrapper — canChooseFiles:false should set SELECT_FOLDER action
but may need upstream fix for correct title.

ui-electrobun/src/mainview/PathBrowser.svelte

@@ -56,7 +56,7 @@
     try {
       const home = await resolveHome();
       const expandedPath = dirPath.replace(/^~/, home);
-      const result = await appRpc.request['files.list']({ path: expandedPath });
+      const result = await appRpc.request['files.browse']({ path: expandedPath });
       if (result?.error) {
         error = result.error;
         entries = [];