fix(vegas): refresh scroll buffer on live score updates (#299)

* fix(vegas): refresh scroll buffer when plugins report live data updates

should_recompose() only checked for cycle completion or staging buffer
content, but plugin updates go to _pending_updates — not the staging
buffer. The scroll display kept showing the old pre-rendered image
until the full cycle ended, even though fresh scores were already
fetched and logged.

Add has_pending_updates() check so hot_swap_content() triggers
immediately when plugins have new data.

Fixes #230

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

* fix(vegas): scope hot-swap to visible segments; use monotonic clock

1. Replace has_pending_updates() with has_pending_updates_for_visible_segments()
   so hot_swap_content() only fires when a pending update affects a plugin that
   is actually in the active scroll buffer (with images). Avoids unnecessary
   recomposition when non-visible plugins report updates.

2. Switch all display-loop timing (start_time, elapsed, _next_live_priority_check)
   from time.time() to time.monotonic() to prevent clock-stepping issues from
   NTP adjustments on Raspberry Pi.

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

---------

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

src/vegas_mode/stream_manager.py

@@ -199,6 +199,21 @@ class StreamManager:
 
         logger.debug("Plugin %s marked for update", plugin_id)
 
+    def has_pending_updates(self) -> bool:
+        """Check if any plugins have pending updates awaiting processing."""
+        with self._buffer_lock:
+            return len(self._pending_updates) > 0
+
+    def has_pending_updates_for_visible_segments(self) -> bool:
+        """Check if pending updates affect plugins currently in the active buffer."""
+        with self._buffer_lock:
+            if not self._pending_updates:
+                return False
+            active_ids = {
+                seg.plugin_id for seg in self._active_buffer if seg.images
+            }
+            return bool(active_ids & self._pending_updates.keys())
+
     def process_updates(self) -> None:
         """
         Process pending plugin updates.