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_on_demand_pinning_and_restart.py

@@ -99,6 +99,31 @@ class TestPinSurvivesARestart:
         assert set(c.on_demand_modes) == {'app_a', 'app_b', 'app_c'}
 
 
+class TestASecondRequestKeepsTheResumePoint:
+    """Clearing returns to where the normal rotation was, not the last request.
+
+    A second start while on-demand was showing overwrote the saved resume
+    index with the first request's mode, so stopping resumed rotation there.
+    """
+
+    def test_clear_resumes_the_original_rotation(self, test_display_controller):
+        c = test_display_controller
+        _plugin_with_modes(c, 'clock', ['clock'])
+        _plugin_with_modes(c, 'weather', ['weather'])
+        _plugin_with_modes(c, 'stocks', ['stocks'])
+        c.available_modes = ['clock', 'weather', 'stocks']
+        c.current_mode_index = 0
+        c.current_display_mode = 'clock'
+
+        c._activate_on_demand({'plugin_id': 'weather', 'mode': 'weather'})
+        c._activate_on_demand({'plugin_id': 'stocks', 'mode': 'stocks'})
+        assert c.current_display_mode == 'stocks'
+
+        c._clear_on_demand(reason='requested-stop')
+        assert c.current_mode_index == 0
+        assert c.current_display_mode == 'clock'
+
+
 class TestRestartDoesNotStarveTheOtherPlugins:
     """Restarting mid-on-demand used to load only the on-demand plugin.