Verified owners get confirmation email; broken thumbnails hidden

Added

• Self-serve listing: verified owners now receive a confirmation email when their domain claim is first accepted. The claim panel shows promotion eligibility tier (live feed/GitHub/App Store vs. queued page/file scan) when promotion is available, or a status note when it isn't — no more dead "Enable tracking" button.

Fixed

• Several browser-side flows — signing in, domain ownership claim, and listing promote — were failing due to CORS gaps; all resolved.
• Broken media thumbnails now hide cleanly instead of leaving jagged icons, orphaned play badges, or empty click targets on cards across the feed, search, collections, and live stream.
• /docs/api/errors now loads — the sidebar link existed but the page route was missing.