feat(events): schedule, recurrence and the calendar (Phase 4)

The four closed recurrence shapes computed in the definition's own IANA zone,
a fourteen-day materialisation horizon with projections beyond it, series as a
managed thing, and the admin calendar that replaces the plugin this feature
exists to replace. An event now happens on its own.

No schema change: Phase 1 built every column this needed.

- events/recurrence.js is the ONE place an occurrence is computed, so the
  runner's expansion and the calendar's forecast cannot disagree. No date
  library added — Node ships the tzdata one would vendor, behind Intl.
- The runner's materialise leg is now two halves: expand, then sweep. The
  window starts at `now - grace`, so an occurrence nobody could have seen is
  never invented retroactively; the horizon is what makes the missed sweep
  mean anything for a recurrence.
- Publishing is the schedule switch and archiving turns it off, and publishing
  re-pins every occurrence that has not started.
- A projection is never drawn over an instant a run occupies, so a cancelled
  occurrence does not reappear as a forecast.

54 new tests, incl. the DST fixture set the plan asked for and three new
statements proved against a real MariaDB. Suite 1768/1711/56 skipped/1 fail
(pre-existing CRLF). Walked end to end on the local review stack.

Docs: RunicGateway/docs#PENDING

Co-Authored-By: Claude <noreply@anthropic.com>

client/src/App.jsx

@@ -50,6 +50,7 @@ import EngagementSendLog from './routes/admin/views/EngagementSendLog.jsx'
 import EngagementSuppressions from './routes/admin/views/EngagementSuppressions.jsx'
 import EngagementRetention from './routes/admin/views/EngagementRetention.jsx'
 import EventsAdmin from './routes/admin/views/EventsAdmin.jsx'
+import EventsCalendar from './routes/admin/views/EventsCalendar.jsx'
 import EventEditor from './routes/admin/views/EventEditor.jsx'
 import EventRun from './routes/admin/views/EventRun.jsx'
 import TeamsAdmin from './routes/admin/views/TeamsAdmin.jsx'
@@ -204,6 +205,7 @@ export default function App() {
                   route it calls. `runs/:runId` is declared before `:id` so the
                   literal segment is never read as a definition id. */}
               <Route path="events" element={<EventsAdmin />} />
+              <Route path="events/calendar" element={<EventsCalendar />} />
               <Route path="events/runs/:runId" element={<EventRun />} />
               <Route path="events/new" element={<EventEditor />} />
               <Route path="events/:id" element={<EventEditor />} />