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>

src/matrix_support.py

@@ -74,6 +74,13 @@ MAPPING_OUTPUTS: Dict[str, int] = {
     'classic-pi1': 1,
 }
 
+#: The refresh cap (``display.hardware.limit_refresh_rate_hz``) when config
+#: omits it -- config/config.template.json's value. DisplayManager passes it to
+#: the library and reports it as ``refresh_hz`` for scroll pacing, so the two
+#: must be the same number: they were 90 and 100, and pacing solved against a
+#: rate the panel was capped below.
+DEFAULT_REFRESH_LIMIT_HZ = 100
+
 #: What DisplayManager passes when a key is missing from display.hardware /
 #: display.runtime. Config migration normally fills these from
 #: config/config.template.json first, so they rarely apply.
@@ -81,7 +88,7 @@ DISPLAY_MANAGER_DEFAULTS: Dict[str, Any] = {
     'rows': 32, 'cols': 64, 'chain_length': 2, 'parallel': 1,
     'hardware_mapping': 'adafruit-hat-pwm', 'brightness': 90, 'pwm_bits': 10,
     'pwm_lsb_nanoseconds': 150, 'led_rgb_sequence': 'RGB',
-    'row_address_type': 0, 'multiplexing': 0, 'limit_refresh_rate_hz': 90,
+    'row_address_type': 0, 'multiplexing': 0, 'limit_refresh_rate_hz': DEFAULT_REFRESH_LIMIT_HZ,
     'gpio_slowdown': 3,
 }