Add listen_events table to record opens, plays and listen duration per
share link. Public POST/PATCH endpoints for fire-and-forget tracking
from the listen page; authenticated GET analytics endpoint aggregates
per version. Listen page gains optional name prompt after first play
and sendBeacon on unload. Track page gains Analytics tab with stats
grid and per-listener event list.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
