🤖 Workspace actions: comment follow-ups from #6461 #6518

Comment-only follow-ups from the final independent check of #6461 (Workspace actions leftovers). None changes behavior.

1. src/browser/components/WorkspaceMenuBar/WorkspaceHeaderTitle.tsx: the doc comment of WorkspaceHeaderTitleInput ("Enter or leaving the field saves, Escape cancels…") now sits above reportSaveError. Move it back above WorkspaceHeaderTitleInput.
2. Same file, useSaveOnUnmount: the comment names only the workspace switch, but the save runs on any unmount while the draft is changed. Reword it (the behavior matches leaving the field).
3. WorkspaceActionsMenuContent.tsx isInMenuPopover: the ?? root fallback is unreachable today (both callers mount the menu inside Radix PopoverContent). Optionally make it fail closed if a future caller mounts the menu outside a dialog.

Owner: the coordinator desk. Pick up with the next change to these files.

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