docs(plugin-api): fix extra_small_font size, cache metric key and scroll pacing example

- PLUGIN_API_REFERENCE: extra_small_font loads at 7, not 6 (crisp_size
  snaps it, src/display_manager.py); get_cache_metrics() returns
  cache_hit_rate, not hit_rate (src/cache/cache_metrics.py).
- ADVANCED_PLUGIN_DEVELOPMENT: the basic scrolling example slept in a loop
  and never passed frame_hold; use ScrollHelper + scroll_config.configure()
  and set_scrolling_state(True, frame_hold=...) as PLUGIN_API_REFERENCE does.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/ADVANCED_PLUGIN_DEVELOPMENT.md

@@ -97,31 +97,53 @@ For plugins that scroll content (tickers, news feeds, etc.), use scrolling state
 
 ### Basic Scrolling Implementation
 
+Scroll with `ScrollHelper`, configured by `src.common.scroll_config`, and
+render one frame per `display()` call. Don't pace the scroll with
+`time.sleep()`: `update_display()` blocks on the panel's
+vsync, which is what paces a scroll. Pass the `frame_hold` that
+`scroll_config.configure()` returned to `set_scrolling_state()`, or the
+scroll runs faster than the configured speed (see
+`set_scrolling_state()` in [PLUGIN_API_REFERENCE.md](PLUGIN_API_REFERENCE.md)).
+
 ```python
+from PIL import Image, ImageDraw
+
+from src.common import scroll_config
+from src.common.scroll_helper import ScrollHelper
+
+def __init__(self, *args, **kwargs):
+    super().__init__(*args, **kwargs)
+    self.scroll_helper = ScrollHelper(
+        self.display_manager.width, self.display_manager.height, self.logger)
+    self.scroll_settings = scroll_config.configure(
+        self.scroll_helper,
+        plugin_config=self.config,
+        global_config=self.global_config,
+        display_manager=self.display_manager,
+        plugin_logger=self.logger,
+    )
+
+def _build_scroll_image(self, text):
+    font = self.display_manager.regular_font
+    width = self.display_manager.get_text_width(text, font)
+    img = Image.new("RGB", (width, self.display_manager.height))
+    ImageDraw.Draw(img).text((0, 0), text, font=font, fill=(255, 255, 255))
+    self.scroll_helper.set_scrolling_image(img)
+
 def display(self, force_clear=False):
-    if force_clear:
+    if force_clear or self.scroll_helper.cached_image is None:
-        self.display_manager.clear()
+        self._build_scroll_image(
-    
+            "This is a long scrolling message that needs to scroll across the display...")
-    # Mark as scrolling
+
-    self.display_manager.set_scrolling_state(True)
+    # Mark as scrolling (calling it every frame is fine)
-    
+    self.display_manager.set_scrolling_state(
-    try:
+        True, frame_hold=self.scroll_settings.frame_hold)
-        # Scroll content
+    self.scroll_helper.update_scroll_position()
-        text = "This is a long scrolling message that needs to scroll across the display..."
+    self.display_manager.image = self.scroll_helper.get_visible_portion()
-        text_width = self.display_manager.get_text_width(text, self.display_manager.regular_font)
+    self.display_manager.update_display()
-        display_width = self.display_manager.width
+
-        
+    if self.scroll_helper.is_scroll_complete():
-        # Scroll from right to left
+        # Mark as not scrolling when done
-        for x in range(display_width, -text_width, -2):
-            self.display_manager.clear()
-            self.display_manager.draw_text(text, x=x, y=16, color=(255, 255, 255))
-            self.display_manager.update_display()
-            time.sleep(0.05)
-            
-            # Update scroll activity timestamp
-            self.display_manager.set_scrolling_state(True)
-    finally:
-        # Always mark as not scrolling when done
         self.display_manager.set_scrolling_state(False)
 ```
 

docs/PLUGIN_API_REFERENCE.md

@@ -620,7 +620,7 @@ The Display Manager provides several pre-loaded fonts:
 display_manager.regular_font      # Press Start 2P, size 8
 display_manager.small_font        # Press Start 2P, size 8
 display_manager.calendar_font     # 5x7 BDF font
-display_manager.extra_small_font  # 4x6 TTF font, size 6
+display_manager.extra_small_font  # 4x6 TTF font, size 7 (6 snapped to its pixel grid)
 display_manager.bdf_5x7_font     # Alias for calendar_font
 ```
 
@@ -854,12 +854,12 @@ for file_info in files:
 
 Get cache performance metrics.
 
-**Returns**: Dictionary with cache statistics (hits, misses, hit rate, etc.)
+**Returns**: Dictionary with cache statistics (`total_requests`, `cache_hit_rate`, `background_hit_rate`, `api_calls_saved`, `average_fetch_time`, etc.)
 
 **Example**:
 ```python
 metrics = self.cache_manager.get_cache_metrics()
-self.logger.info(f"Cache hit rate: {metrics['hit_rate']:.2%}")
+self.logger.info(f"Cache hit rate: {metrics['cache_hit_rate']:.2%}")
 ```
 
 #### `get_memory_cache_stats() -> Dict[str, Any]`