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/font_manager.py

@@ -498,6 +498,7 @@ class FontManager:
         self.performance_stats["cache_misses"] += 1
 
         # Load font
+        shareable = True
         font_path = self.font_catalog.get(family)
         if not font_path:
             logger.warning(f"Font family '{family}' not found")
@@ -507,6 +508,7 @@ class FontManager:
             try:
                 if font_path.endswith('.bdf'):
                     font = self._load_bdf_font(font_path, size_px)
+                    shareable = False
                 else:
                     font = load_truetype(font_path, size_px)
             except Exception as e:
@@ -516,7 +518,11 @@ class FontManager:
                 self.performance_stats["failed_loads"] += 1
                 font = ImageFont.load_default()
 
-        self.font_cache[cache_key] = font
+        # A BDF face is not cached here: font_cache is shared by every
+        # thread, and a freetype.Face must never be (see load_bdf_face, which
+        # already caches BDF faces per thread).
+        if shareable:
+            self.font_cache[cache_key] = font
         return font
 
     def _load_bdf_font(self, font_path: str, size_px: int) -> freetype.Face: