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>

src/shared/contracts/ipc.ts

@@ -108,6 +108,8 @@ export interface ElectronApi {
   selectSession(sessionId?: string): Promise<WorkspaceState>;
   setPatternFavorite(input: SetPatternFavoriteInput): Promise<WorkspaceState>;
   setTheme(theme: AppearanceTheme): Promise<WorkspaceState>;
+  openAppDataFolder(): Promise<void>;
+  resetLocalWorkspace(): Promise<WorkspaceState>;
   onWorkspaceUpdated(listener: (workspace: WorkspaceState) => void): () => void;
   onSessionEvent(listener: (event: SessionEventRecord) => void): () => void;
 }