feat: add troubleshooting settings with open app data and reset workspace

Add a Troubleshooting section under a Support nav group in Settings:

- Open App Data Folder: reveals the user-data directory in the OS file
  explorer via shell.openPath.
- Reset Local Workspace: destructive action that deletes workspace.json
  and scratchpad contents, clears the in-memory cache, and reseeds
  defaults. Auth secrets are preserved. Requires two-step confirmation.

New IPC channels, ElectronApi methods, and preload bridge added for
openAppDataFolder and resetLocalWorkspace. Existing electron mock in
tests updated to include shell.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

tests/main/appServiceTooling.test.ts

@@ -18,6 +18,9 @@ mock.module('electron', () => ({
   dialog: {
     showOpenDialog: async () => ({ canceled: true, filePaths: [] }),
   },
+  shell: {
+    openPath: async () => '',
+  },
 }));
 
 mock.module('keytar', () => ({