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

client/test/eventAuthoring.test.js

@@ -252,6 +252,29 @@ test('the form round-trips a definition without losing a step', () => {
   assert.equal(built.payload.concurrencyKey, 'invasion:{region}')
 })
 
+test('`listed` round-trips, and an unlisted event is not quietly re-listed', () => {
+  // The trap this guards is `||` where `??` is meant. A definition an operator
+  // deliberately unlisted sends `listed: false`, and `event?.listed || true`
+  // would put it back on the public calendar on the author's next save — a
+  // surprise event announced by a typo fix.
+  const unlisted = payloadFromForm(
+    formFromDefinition({ title: 'Invasion', listed: false, spec: { schedule: { kind: 'manual' }, phases: [] } }),
+  )
+  assert.equal(unlisted.payload.listed, false)
+
+  const listed = payloadFromForm(
+    formFromDefinition({ title: 'Invasion', listed: true, spec: { schedule: { kind: 'manual' }, phases: [] } }),
+  )
+  assert.equal(listed.payload.listed, true)
+})
+
+test('a new definition defaults to listed', () => {
+  // The column's own default, and the ordinary case: unlisting is the
+  // deliberate act, not listing.
+  const fresh = payloadFromForm(formFromDefinition({ spec: { schedule: { kind: 'manual' }, phases: [] } }))
+  assert.equal(fresh.payload.listed, true)
+})
+
 test('an unchosen onFailure is omitted rather than invented', () => {
   // The server defaults it from the action's risk class, which is the whole
   // reason `risk` is required at registration. A form that posted a value would