feat(events): a trigger can start a run

Rust PLAN_REDESIGNS §14.3.12 (D370), stage 9 of §14.3. A definition's
published version may carry `starts`: a trigger, a condition and a
cooldown. A matching firing creates a run of it, now.

- spec: `starts` validated by the phase gate's own function (same
  grammar, same dormant rule; a dormant start refuses publish), a
  cooldown from 0m to 7d (30m default), at most ten, event.* refused.
- events/starts.js: the emit path's third subscriber, beside dispatch
  and the gate observer. An unverified version starts nothing; one run
  at a time per definition and the cooldown are one conditional UPDATE
  on the new event_trigger_starts table; the occurrence key makes one
  firing reported twice one run. Ignored firings are counted by why.
- event_runs.origin: the firing (trigger, label, time, subject, matched
  condition, declared variables), also on the run.created audit line.
- Editor: a "Started by the game" panel using the gate's condition
  builder, with the ignored-firings line. Run console: "Started because
  ... fired".
- No module contract change and no MODULE_API bump.

Tests: eventStarts (server 21, client 8); eventRunnerSql +7 against a
real MariaDB (75/75); Module-uo proof on uo.champ.boss_up against the
dev database.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E14m6SuuY6i1vASFeGDBeY

client/src/routes/admin/views/EventRun.jsx

@@ -10,6 +10,7 @@ import {
   stepControlsFor,
   describeLogLine,
   describeParams,
+  describeOrigin,
 } from '../../../lib/eventAuthoring.js'
 
 // Admin → Events → the run console (EVENTS.md §I, Phase 3).
@@ -294,6 +295,13 @@ export default function EventRun() {
             {run.rehearsal ? ' · rehearsal' : ''}
             {run.concurrencyKey ? ` · key ${run.concurrencyKey}` : ''}
           </p>
+          {/* Why it exists, when a game firing started it (D370). */}
+          {describeOrigin(run.origin) && (
+            <p className="sans" style={{ margin: '4px 0 0', fontSize: '0.8rem' }}>
+              {describeOrigin(run.origin)}
+              <span className="dim"> · {when(run.origin.occurredAt)}</span>
+            </p>
+          )}
         </div>
         <div style={{ textAlign: 'right' }}>
           <div className="sans" style={{ fontSize: '1rem', color: STATUS_COLOR[run.status] || undefined }}>