feat(sync): split version polling into fast metadata + hourly search schedules

The single 2-minute schedule per artifact paginated the Sonatype REST
component-search on every tick — wasteful for what is nearly always a
"no new versions" answer. Poll maven-metadata.xml every 2 minutes for
fast new-version detection and fall back to full REST pagination once
an hour as a correctness backstop. Metadata can list a version before
its assets are indexed, so a VersionHasAssets probe gates each
candidate to prevent permanent zero-asset ghost rows.

TriggerSync gains ?source=metadata|search for on-demand routing.

Signed-off-by: Gabriel Harris-Rouquette <gabizou@me.com>

Author: gabizou