feat(events): the public calendar, event pages and participation history (Phase 14a)

The anonymous surface an event was always for: GET /public/events,
/public/events/:slug and /public/events/series/:slug, plus
GET /player/events/history, and the four screens over them.

Four org-lead decisions taken up front: split Phase 14 into 14a (website)
and 14b (the app); add a `listed` flag rather than letting `state` mean both
schedulable and announced; put the `events` capability string in the version
block rather than publishing core as a pseudo-module; and drop "venue" from
the spec rather than adding a field nothing had ever built.

`listed` is announcement, not permission. Publishing is what makes a
definition runnable, so without a separate flag a surprise event would have
to be advertised in order to be allowed to happen. It is a column, a switch
in Phase 13's editor, and three SQL predicates -- never a filter applied
after a read, which works exactly as well until the first caller that forgets.

The public shapes are a projection, and the projection is the security
boundary: nothing is spread, so a column added to event_runs next year does
not ride out through it. The spec, health, cleanup, claims, errors and
member_key are all absent by construction.

The six public event triggers gained `eventUrl` (version 1 -> 2), carrying
?run= because the page lives at the definition's slug while every trigger is
about one occurrence. notify.event-started gained the button, at seedVersion 2.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016wDDVXWMDz82WqE1i969r4

server/src/router/v1/public/index.js

@@ -22,6 +22,7 @@ const wikiRouter = require('./wiki.router')
 const pagesRouter = require('./pages.router')
 const modulesRouter = require('./modules.router')
 const teamsRouter = require('./teams.router')
+const eventsRouter = require('./events.router')
 const engagementRouter = require('./engagement.router')
 const siteRouter = require('./site.router')
 
@@ -42,6 +43,10 @@ publicRouter.use('/modules', modulesRouter)
 // is what populates it (TEAMS.md §10.3). Site-mode gated per route, like the
 // content above it.
 publicRouter.use('/teams', teamsRouter)
+// Events. A core prefix like /teams: the calendar, the event page and the arc
+// are core's surface even when every step an event dispatches belongs to a
+// module. Site-mode gated per route, like the content above it.
+publicRouter.use('/events', eventsRouter)
 // The unauthenticated half of the engagement system: today exactly the
 // unsubscribe pair. Its own prefix rather than a Teams sub-path, because what a
 // token names is a channel and a scope and a scope is not always a Team