fix(display): thread-safety for deferred updates, BDF faces and follower image; one refresh default (#652)

- DisplayManager.defer_update()/process_deferred_updates(): one lock around
  every queue mutation (appends from the update thread were lost to the
  render thread's filter/slice reassignments); callables run outside it.
- FontManager and element_style no longer cache BDF freetype.Face objects
  process-wide (load_bdf_face caches them per thread); element_style's LRU
  is locked against get/move_to_end vs eviction races.
- limit_refresh_rate_hz default is one constant, DEFAULT_REFRESH_LIMIT_HZ =
  100 (the template's), for the library options, refresh_hz, the matrix
  guard, Vegas and scroll_config. Previously a missing key capped the panel
  at 90 while pacing assumed 100.
- Sync follower: the TCP thread queues the leader's scroll image; the render
  thread swaps image/array/width in between frames.
- update_display() error log rate-limited (traceback first, then once a
  minute with a count); swallowed DisplayController exceptions log at DEBUG.
- Root display_controller.py runs run.py via runpy.
- stream_manager: correct the RLock release comments; merge duplicate if.

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

display_controller.py

@@ -1,12 +1,20 @@
 #!/usr/bin/env python3
+"""Legacy entry point: runs ``run.py``, which is the one to use.
+
+``python3 run.py`` (``-e`` for the emulator, ``-d`` for debug logging) is how
+the display service and the docs start LEDMatrix. This file used to import
+``src.display_controller.main`` directly, which skipped what run.py sets up
+first -- ``sys.dont_write_bytecode`` (root-owned ``__pycache__`` in plugin
+directories blocks the web service from updating them), the ``-e``/``-d``
+flags, and the logging configuration. It now runs run.py exactly as
+``python3 run.py`` would, with the same arguments.
+"""
 
 import os
-import sys
-
-# Add the project root directory to Python path
-sys.path.append(os.path.dirname(os.path.abspath(__file__)))
-
-from src.display_controller import main
+import runpy
 
 if __name__ == "__main__":
-    main() 
+    runpy.run_path(
+        os.path.join(os.path.dirname(os.path.abspath(__file__)), "run.py"),
+        run_name="__main__",
+    )