Changing the sync folder does not restart the file-transfer watcher

[offbyonebit]

Severity: medium
Type: bug
Location: clipsync/main.py — ClipSyncApp._on_folder_changed() (~line 580)

Problem: When the user changes the sync folder, _on_folder_changed() stops and restarts ClipboardSync but leaves the old FileTransfer instance watching the old folder. Outgoing files still go to the new folder, but incoming files in the new folder are never observed, so received-file notifications stop working.

Suggested fix: Also stop the existing FileTransfer and create a new one watching the new folder before restarting the clipboard engine.

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_{Filed from a full-source audit of the repo (2026-07-29). Reported by the audit but not independently confirmed - verify the cited code before acting on it.}