Move the sync / network / store-transfer verbs — serve, clone, open, pack, pull, push, sync, remote — together with the helpers and tests private to them out of main.zig into a new src/cmd/sync.zig. This is a pure behaviour-preserving move: every relocated line is byte-identical to its main.zig source; only cmd/sync.zig's import prologue and the handlers' pub visibility are new.

Helpers still shared with other verbs stay in main.zig, now made pub and aliased back in cmd/sync.zig so the moved bodies call them by their original unqualified names. The verb-dispatch switch stays in main.zig and calls into the new file; main.zig's test block imports it so the moved inline tests keep running.

No behaviour change: the full test count is unchanged and the dead-file guard reaches cmd/sync.zig through the dispatch import, with no allowlist entry. closed check-in: 254575cbd8 user: dmestas tags: s2-sync