Populate scanner feeds from the public ProScan directory

[ralyodio]

The scanner pages shipped without an enabled feed source, leaving the live catalog empty. This adds a default ProScan directory importer so deployment automatically starts collecting real scanner listings.

• Import public directory listings every 15 minutes and discover explicitly advertised audio and playlist URLs from a bounded, rotating batch of player pages.
• Show player, audio, and playlist links with operator/source attribution on scanner detail pages.
• Respect robots policies, validate and pin public DNS addresses, and bound redirects, response size, and timeouts. Preserve discovered links across transient failures and mark removed listings inactive.
• Preserve location labels; leave geographic coverage unknown where the directory supplies no coordinates.

Validation: 46 targeted tests pass; lint, app build, and diff checks pass. A fetched live directory snapshot produced 101 usable listings, and real player HTML yielded advertised audio/playlist URLs. Production ingestion still needs verification after deployment.