extract sync orchestration into sync.js, unify on sync.tick heartbeat

caldav.js was carrying the core sync timer, autosync toggle, relay
settings and every poller hook alongside its actual CalDAV/calendar
config concerns. Split out:

- New sync.js owns the single background timer, header Sync button,
  autosync pause toggle, configurable interval, and emits `sync.tick`
  so plugins can fan out without their own setIntervals.
- collab-buckets + chat now subscribe to sync.tick instead of running
  their own pollers, so the manual Sync button refreshes them too and
  the Autosync pause actually pauses everything.
- Replace the number input for sync interval with a stepped slider
  (5s..1h snap points) and a live label, bumped to 1.9.2.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

public/plugins/chat/chat.js

@@ -410,6 +410,12 @@ function init() {
             restartPoll();
         }
     });
+
+    // Also refresh on the global sync heartbeat. Our own timer keeps
+    // the faster flyout-open cadence (UX-specific); tick guarantees
+    // that the header Sync button refreshes chat too, even when the
+    // flyout is closed and our own timer sits at 20s.
+    hyprcrd.hooks?.on?.('sync.tick', () => { pollOnce().catch(() => {}); });
 }
 
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