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>

test/test_matrix_support.py

@@ -122,4 +122,24 @@ def test_display_manager_defaults_match_display_manager():
     for field, value in ms.DISPLAY_MANAGER_DEFAULTS.items():
         if field in ('rows', 'cols', 'chain_length', 'parallel'):
             continue  # read through display_geometry's DEFAULT_* constants
+        if field == 'limit_refresh_rate_hz':
+            assert "get('limit_refresh_rate_hz', DEFAULT_REFRESH_LIMIT_HZ)" in source
+            continue
         assert f"get('{field}', {value!r})" in source, field
+
+
+def test_missing_refresh_limit_applies_the_rate_pacing_assumes():
+    """With limit_refresh_rate_hz absent the library was capped at 90 Hz while
+    refresh_hz (what scroll pacing solves against) reported 100. One default,
+    and it is the template's."""
+    import os
+    from types import SimpleNamespace
+    os.environ.setdefault("EMULATOR", "true")  # import off-Pi, as other modules do
+    from src.display_manager import DisplayManager
+
+    options = DisplayManager.apply_matrix_options(SimpleNamespace(), {})
+    reported = DisplayManager.refresh_hz.fget(SimpleNamespace(config={}))
+    assert options.limit_refresh_rate_hz == reported
+    template = json.loads((REPO_ROOT / 'config' / 'config.template.json').read_text(encoding='utf-8'))
+    assert options.limit_refresh_rate_hz == template['display']['hardware']['limit_refresh_rate_hz']
+    assert ms.DISPLAY_MANAGER_DEFAULTS['limit_refresh_rate_hz'] == options.limit_refresh_rate_hz