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/preload/index.ts

@@ -34,7 +34,9 @@ const api: ElectronApi = {
   selectProject: (projectId) => ipcRenderer.invoke(ipcChannels.selectProject, projectId),
   selectPattern: (patternId) => ipcRenderer.invoke(ipcChannels.selectPattern, patternId),
   selectSession: (sessionId) => ipcRenderer.invoke(ipcChannels.selectSession, sessionId),
-  onWorkspaceUpdated: (listener) => {
+  openAppDataFolder: () => ipcRenderer.invoke(ipcChannels.openAppDataFolder),
+  resetLocalWorkspace: () => ipcRenderer.invoke(ipcChannels.resetLocalWorkspace),
+  onWorkspaceUpdated:(listener) => {
     const handler = (_event: Electron.IpcRendererEvent, workspace: Awaited<ReturnType<ElectronApi['loadWorkspace']>>) =>
       listener(workspace);