feat(scheduler): add Scheduled Jobs UI

- scheduler-ui.js: job list + create/edit form + Run Now/Enable/Disable/Delete,
  reacting to scheduler:* SSE events; same-agent Run Now warning
- index.html: "⏰ Schedules" toolbar button + #schedulerModal + script include
- constants.js / app.js: frontend SSE event constants + handler map entries
- styles.css: scheduler row/badge/form styles

Follows Codeman's vanilla-JS mixin + .modal/.form-row conventions.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Rp7JhmQXcYJhmxFMdZuuah

src/web/public/constants.js

@@ -276,6 +276,12 @@ const SSE_EVENTS = {
   SCHEDULED_LOG: 'scheduled:log',
   SCHEDULED_DELETED: 'scheduled:deleted',
 
+  // Scheduled jobs (cron-style scheduler)
+  SCHEDULER_JOBS_CHANGED: 'scheduler:jobsChanged',
+  SCHEDULER_JOB_DELETED: 'scheduler:jobDeleted',
+  SCHEDULER_RUN_CREATED: 'scheduler:runCreated',
+  SCHEDULER_RUN_UPDATED: 'scheduler:runUpdated',
+
   // Respawn
   RESPAWN_STARTED: 'respawn:started',
   RESPAWN_STOPPED: 'respawn:stopped',