Add sync CLI commands for managing and running synced playlists

[semohr]

Summary

Adds the plistsync sync subcommand group with:

• sync create (alias mk): create a named synced playlist
• sync remove (alias rm): remove a synced playlist (with confirmation prompt)
• sync list (alias ls): list all synced playlists
• sync register: link an existing service playlist to a synced playlist
• sync show: show the per-playlist track overview of a synced playlist
• sync run: run the synchronisation for one or all synced playlists

Details

• Commands accept a synced playlist by name or ID; ambiguous/missing matches raise a clear error.
• Shell autocompletion for synced playlist names and IDs on applicable arguments.
• --json output on create, remove, list, and register for scripting.
• run with no argument synchronises all registered synced playlists.
• Refactors cli setup to use its own module for the commands

TODO

• Improve test coverage

[github-actions]

Thank you for the PR! The changelog has not been updated, so here is a friendly reminder to check if you need to add an entry.

[codecov]

Codecov Report

❌ Patch coverage is 99.10314% with 2 lines in your changes missing coverage. Please review.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
plistsync/__main__.py	0.00%	2 Missing ⚠️

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