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

server/src/model/events/eventRuns.db.js

@@ -15,7 +15,13 @@
 const { query } = require('../../utils/db')
 const { parseJson } = require('./eventJson')
 
-const hydrate = (row) => row && { ...row, params: parseJson(row.params, null), rehearsal: Boolean(row.rehearsal) }
+const hydrate = (row) =>
+  row && {
+    ...row,
+    params: parseJson(row.params, null),
+    origin: parseJson(row.origin, null),
+    rehearsal: Boolean(row.rehearsal),
+  }
 
 // The statuses a run never leaves. A transition INTO one of these stamps
 // `ended_at` and drops the claim, and only rows in one of them are eligible for
@@ -90,8 +96,8 @@ const materialise = async (run) => {
   const result = await query(
     `INSERT IGNORE INTO event_runs
        (definition_id, version_id, scope, scheduled_for, timezone, concurrency_key,
-        params, rehearsal, started_by)
-     VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?)`,
+        params, rehearsal, started_by, origin)
+     VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)`,
     [
       run.definition_id,
       run.version_id,
@@ -102,6 +108,8 @@ const materialise = async (run) => {
       run.params === null || run.params === undefined ? null : JSON.stringify(run.params),
       run.rehearsal ? 1 : 0,
       run.started_by,
+      // Why the run exists when a trigger started it (D370); NULL otherwise.
+      run.origin ? JSON.stringify(run.origin) : null,
     ],
   )
   return Number(result?.affectedRows || 0) === 1 ? result.insertId : null