Cookbook scheduler: inline settings card at the top of the Cookbook tab

The earlier scheduler commit shipped the backend + Schedule modal but left the feature dormant — no way to toggle it from the UI. This adds the missing knob:

* DEFAULT_SETTINGS gains `cookbook_scheduler_enabled` (False) and `cookbook_schedule_calendar_href` ("") so `/api/auth/settings` POST will actually persist them. Without this, the POST silently dropped unknown keys.

* cookbookSchedule.js gains a self-contained settings card injected at the top of the Cookbook tab body whenever the cookbook modal opens. Card contents:
  - Enable toggle (writes cookbook_scheduler_enabled)
  - Calendar dropdown populated from /api/calendar/calendars (writes cookbook_schedule_calendar_href)
  - Status line: off / pick-a-calendar / N scheduled in next 24h · M running now · K skipped
  - "Reconcile now" button that POSTs /api/cookbook/schedule/reconcile-now

* The same module reveals/hides the Schedule… buttons on serve panels whenever the feature flag changes, so toggling on immediately surfaces the schedule UI without a refresh.

Settings UI lives in cookbookSchedule.js (not settings.js) so the entire scheduler surface — backend, reconciler, modal, settings — collapses cleanly: delete src/cookbook_scheduler.py + routes/cookbook_schedule_routes.py + static/js/cookbookSchedule.js, drop the two DEFAULT_SETTINGS keys, and the two app.py registration lines, and the feature is gone.

src/settings.py

@@ -159,6 +159,12 @@ DEFAULT_SETTINGS = {
         "admin_panel": "ctrl+shift+u",
         "cancel": "escape",
     },
+    # Cookbook scheduler (calendar-driven serve windows). Off by default;
+    # the inline card in the Cookbook tab flips this. When true, the
+    # reconciler at src/cookbook_scheduler.py reads events from the
+    # designated calendar and auto-launches/kills serves.
+    "cookbook_scheduler_enabled": False,
+    "cookbook_schedule_calendar_href": "",
 }
 
 DEFAULT_FEATURES = {