Disable harvesting from archived OGM repositories

[ewlarson]

Archived BTAA repositories remained enabled because discovery filtered them out before updating the catalog. Starting a harvest also overwrote saved repository settings. This change reconciles archived repositories as disabled and preserves those settings, allowing the active geobtaa repository to supply migrated metadata.

• Skip disabled or archived sources when scheduling and executing harvests, including already queued jobs.
• Handle repository archive webhooks and exclude archived checkouts from standalone record streaming.
• Retain previously harvested records; disabling a repository does not delete its data.

Validation: 21 focused tests passed covering discovery, scheduling, harvest execution, search synchronization, webhooks, and standalone streaming. Ruff and diff checks passed. Database integration tests were not run because local services are stopped.

After merge, cut a new release and deploy it to production, then refresh the repository catalog, pull the current metadata, and reindex. Production has only been inspected; no deployment, metadata refresh, or reindex was performed for this PR.

Fixes #15.