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/ports/cron-port.ts

@@ -0,0 +1,10 @@
+/**
+ * @fileoverview Cron port — exposes the CronService to
+ * route handlers via the shared route context.
+ */
+
+import type { CronService } from '../../cron/cron-service.js';
+
+export interface CronPort {
+  readonly cron: CronService;
+}

src/web/ports/index.ts

@@ -13,4 +13,4 @@ export type { ConfigPort } from './config-port.js';
 export type { InfraPort, ScheduledRun } from './infra-port.js';
 export type { AuthPort } from './auth-port.js';
 export type { OrchestratorPort } from './orchestrator-port.js';
-export type { SchedulerPort } from './scheduler-port.js';
+export type { CronPort } from './cron-port.js';

src/web/ports/scheduler-port.ts

@@ -1,10 +0,0 @@
-/**
- * @fileoverview Scheduler port — exposes the cron-style SchedulerService to
- * route handlers via the shared route context.
- */
-
-import type { SchedulerService } from '../../scheduler/scheduler-service.js';
-
-export interface SchedulerPort {
-  readonly scheduler: SchedulerService;
-}