refactor(cron): rename scheduler feature to cron

Rename the recurring-jobs feature scheduler->cron to disambiguate from the
legacy ScheduledRun system (/api/scheduled), which is left untouched:

- ScheduledJob->CronJob, SchedulerService->CronService
- /api/scheduler/jobs -> /api/cron/jobs; SSE scheduler:* -> cron:*
- state keys cronJobs/cronJobRuns
- files moved to src/cron/, cron-routes.ts, cron-port.ts, types/cron.ts
- frontend cron-ui.js, #cronModal, menu "Cron"
- docs moved to docs/cron-discovery.md + docs/cron-build-brief.md, README guides
- new tests: cron-service.test.ts, cron-time.test.ts

Green: tsc, lint, frontend-syntax, format, 30 cron + 9 legacy scheduled-runs tests.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PmvZR12aX2v8K7YhqxPUAU

src/web/sse-events.ts

@@ -240,16 +240,16 @@ export const ScheduledLog = 'scheduled:log' as const;
 /** Scheduled run deleted. */
 export const ScheduledDeleted = 'scheduled:deleted' as const;
 
-// ─── Scheduled Jobs (cron-style scheduler) ───────────────────────────────────
+// ─── Cron Jobs ───────────────────────────────────
 
 /** The scheduled-jobs list changed (created/updated/enabled/run-status). Payload: { jobs }. */
-export const SchedulerJobsChanged = 'scheduler:jobsChanged' as const;
+export const CronJobsChanged = 'cron:jobsChanged' as const;
 /** A scheduled job was deleted. Payload: { id }. */
-export const SchedulerJobDeleted = 'scheduler:jobDeleted' as const;
-/** A scheduled-job run (history record) was created. Payload: ScheduledJobRun. */
-export const SchedulerRunCreated = 'scheduler:runCreated' as const;
-/** A scheduled-job run (history record) was updated. Payload: ScheduledJobRun. */
-export const SchedulerRunUpdated = 'scheduler:runUpdated' as const;
+export const CronJobDeleted = 'cron:jobDeleted' as const;
+/** A scheduled-job run (history record) was created. Payload: CronJobRun. */
+export const CronRunCreated = 'cron:runCreated' as const;
+/** A scheduled-job run (history record) was updated. Payload: CronJobRun. */
+export const CronRunUpdated = 'cron:runUpdated' as const;
 
 // ─── Teams ───────────────────────────────────────────────────────────────────
 
@@ -480,11 +480,11 @@ export const SseEvent = {
   ScheduledLog,
   ScheduledDeleted,
 
-  // Scheduled jobs (cron-style scheduler)
-  SchedulerJobsChanged,
-  SchedulerJobDeleted,
-  SchedulerRunCreated,
-  SchedulerRunUpdated,
+  // Cron jobs
+  CronJobsChanged,
+  CronJobDeleted,
+  CronRunCreated,
+  CronRunUpdated,
 
   // Teams
   TeamCreated,