Plumbs libfossil's `Tags []TagSpec` primitive through `hub.CommitOpts` so callers can land a checkin on a non-current branch (or attach any other tag) without going around the EdgeSync API to libfossil.

Fossil branches are propagating tags: `branch=<name>` + `sym-<name>=*` together place a checkin on a branch. Exposing `Tags` rather than a git-flavored `Branch string` keeps the API fossil-native and is strictly more expressive — any tag (closed, release, custom) can be attached at commit time, not just branch creators.

Empty `Tags` preserves the existing trunk-default behavior; current callsites compile and run unchanged.

Closes #147 check-in: 7536beb856 user: [email protected] tags: trunk, v0.0.15