Open mic event pages

Recurring weekly open jams (listed under Jams) each get their own

event page: `/jams/<id>`. It shows the schedule ("Every Tuesday,

7:00 PM – 10:00 PM"), the venue, the host, contact info, the next few

occurrences, and who's coming.

Weekly auto-rollover

The page always shows the next four occurrences, and it **rolls forward

by itself**: once this week's jam has passed, next week's takes its

place. Nobody has to update anything — no cron, no manual rollover.

An occurrence stays "this week" until its end time (or four hours past

start when no end time is set).

Any logged-in user can RSVP — I'm coming from the event page. The

page lists who's coming and your own RSVP state; Cancel RSVP

removes you.

the event page appears automatically once the jam exists.

provided, all-ages or 21+) — it's the first thing newcomers read.

close their jams from the Jams list). Taken-down jams have no page.

and times — if the host changed the night, the page follows the new

schedule automatically.