fix(vegas): restore live plugin-update refresh dropped by sync refactor (#395)

Investigating a user report that Vegas scroll mode doesn't update scores
or game status. Root cause: PR #299 (Mar 28) added a mechanism so a live
score change reached the ticker within a few seconds instead of waiting
for a full scroll cycle -- _tick_plugin_updates_for_vegas() diffed
plugin_last_update timestamps to detect which plugins got fresh data and
called coordinator.mark_plugin_updated() for each, and should_recompose()
checked has_pending_updates_for_visible_segments() to trigger an immediate
hot-swap.

PR #330 (May 14, multi-display wireless sync) refactored both call sites
while adding sync support and silently deleted this entire mechanism --
not just gated it behind the new sync-mode deferral it legitimately
needed, but removed it outright. The result: VegasModeCoordinator.
mark_plugin_updated() and StreamManager.has_pending_updates_for_visible_
segments() have been fully implemented but never called from anywhere
since. Vegas mode's only remaining freshness sources are a 5s content
cache TTL (fine) and full recompose at cycle boundaries, which depending
on min/max_cycle_duration can be minutes away -- so live scores/status
can sit stale far longer than a user would expect from a "live" ticker.

Fix:
- Restored _tick_plugin_updates_for_vegas() in display_controller.py,
  wired as the Vegas coordinator's update callback in place of the plain
  _tick_plugin_updates(). Diffs plugin_last_update before/after the tick
  and calls vegas_coordinator.mark_plugin_updated(plugin_id) for each
  plugin that actually got new data (rather than returning the list, since
  the callback interface no longer consumes a return value).
- Restored the has_pending_updates_for_visible_segments() check in
  render_pipeline.should_recompose(), positioned after (not instead of)
  the sync-mode early return PR #330 added, so standalone installations
  regain immediate refresh while synced leader/follower pairs correctly
  keep deferring hot-swaps to cycle boundaries as PR #330 intended.

Test plan:
- Added test_display_controller_vegas_tick.py and
  test_vegas_render_pipeline_recompose.py -- neither area had any prior
  test coverage, which is very likely why this regression went unnoticed
  for ~2.5 months.
- Verified both new test files fail against the pre-fix code (swapped in
  the current main versions of both files) with exactly the expected
  errors -- AttributeError for the deleted method, and the recompose
  assertion returning False instead of True -- then pass against the fix.
- Confirmed the sync-mode deferral this restoration must not break still
  holds: test_sync_active_defers_pending_updates_to_cycle_boundary.
- Full related suite (test_vegas_plugin_adapter, test_vegas_config,
  test_display_controller_plugin_toggle, test_display_controller_
  optimizations, test_plugin_system): 108 passed, 1 pre-existing failure
  unrelated to this change (test_circuit_breaker, stale mock signature).
- Full CI plugin-safety suite (test_harness, test_visual_rendering,
  test_plugin_matrix): 52 passed, 2 pre-existing skips.

src/vegas_mode/render_pipeline.py

@@ -297,6 +297,8 @@ class RenderPipeline:
         Returns True when:
         - Cycle is complete and we should start fresh
         - Staging buffer has new content
+        - A plugin currently visible in the scroll has pending updated data
+          (e.g. a live score changed) — standalone (non-sync) mode only
         """
         if self._cycle_complete:
             return True
@@ -314,6 +316,12 @@ class RenderPipeline:
         if buffer_status['staging_count'] > 0:
             return True
 
+        # Trigger recompose when pending updates affect visible segments, so
+        # live score/status changes reach the display within a few seconds
+        # instead of waiting for the next full cycle.
+        if self.stream_manager.has_pending_updates_for_visible_segments():
+            return True
+
         return False
 
     def hot_swap_content(self) -> bool: