Problem
`openBookmark` already handles the failure case (file moved/deleted) by showing an error message, but the stale bookmark stays in the list forever — the user has to notice the error and manually remove it every time they click it.
Proposal
- Visually mark bookmarks whose target no longer resolves (e.g. a warning icon/greyed out state) the next time the tree refreshes or a lightweight existence check runs.
- Add a "Remove Broken Bookmarks" command that sweeps the whole list (via `vscode.workspace.fs.stat`) and removes bookmarks pointing at files that no longer exist, with a confirmation showing the count.
Notes
Keep the check lazy/on-demand rather than polling continuously — most workspaces won't have many stale entries and a background `fs.stat` loop isn't worth the cost.
Problem
`openBookmark` already handles the failure case (file moved/deleted) by showing an error message, but the stale bookmark stays in the list forever — the user has to notice the error and manually remove it every time they click it.
Proposal
Notes
Keep the check lazy/on-demand rather than polling continuously — most workspaces won't have many stale entries and a background `fs.stat` loop isn't worth the cost.