fix(display): Vegas resumes after live priority, and six smaller runtime fixes (#644)

- Vegas: a live-priority pause was only lifted from inside run_frame(),
  which returns before that check while paused, so the ticker never came
  back until a restart. run_iteration() now resumes it (the controller
  only calls it when nothing preempts Vegas); start()/stop() clear the
  pause state. Iteration length is timed with the monotonic clock.
- Dim schedule: a per-day disabled day now updates the minute-gate cache,
  so brightness no longer flips back to dim within each minute.
- On-demand: a second request no longer overwrites the rotation resume
  index with the first request's mode.
- Render pipeline: reset() drops the prepared group and deferred queue,
  and a prefetch in flight across a reset discards its result.
- Sync: stop() removes the status file (and the controller's cleanup now
  calls it), standalone removes a stale one at startup, and writes use a
  unique mkstemp temp file.
- render_gate.swap_releases_gil() delegates to frame_timing.
- Stale docstrings/comments corrected.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

test/test_display_controller_cleanup.py

@@ -49,6 +49,31 @@ def test_cleanup_without_vegas_does_not_raise():
     dc.display_manager.cleanup.assert_called_once_with()
 
 
+def test_cleanup_stops_display_sync_after_vegas():
+    # Stopping sync withdraws its status file; left behind, the web UI kept
+    # reporting a connected peer after the display service had stopped.
+    order = []
+    vegas = MagicMock()
+    vegas.cleanup.side_effect = lambda: order.append('vegas')
+    dc = _controller(vegas)
+    dc.sync_manager = MagicMock()
+    dc.sync_manager.stop.side_effect = lambda: order.append('sync')
+
+    dc.cleanup()
+
+    assert order == ['vegas', 'sync']
+
+
+def test_a_failing_sync_stop_does_not_stop_the_rest():
+    dc = _controller(None)
+    dc.sync_manager = MagicMock()
+    dc.sync_manager.stop.side_effect = OSError('boom')
+
+    dc.cleanup()
+
+    dc.display_manager.cleanup.assert_called_once_with()
+
+
 def test_a_failing_vegas_teardown_does_not_stop_the_rest():
     vegas = MagicMock()
     vegas.cleanup.side_effect = RuntimeError('boom')