feat: Implement scrolling camera with layout-aware filtering

- Rename VERTICAL camera mode to FEED (rapid single-item view)
- Add SCROLL camera mode with float accumulation for smooth movie-credits style scrolling
- Add estimate_block_height() for cheap layout calculation without full rendering
- Replace ViewportFilterStage with layout-aware filtering that tracks camera position
- Add render caching to FontStage to avoid re-rendering items
- Fix CameraStage to use global canvas height for scrolling bounds
- Add horizontal padding in Camera.apply() to prevent ghosting
- Add get_dimensions() to MultiDisplay for proper viewport sizing
- Fix PygameDisplay to auto-detect viewport from window size
- Update presets to use scroll camera with appropriate speeds

engine/app.py

@@ -120,7 +120,7 @@ def run_pipeline_mode(preset_name: str = "demo"):
         print(f"  \033[38;5;196mFailed to create display: {display_name}\033[0m")
         sys.exit(1)
 
-    display.init(80, 24)
+    display.init(0, 0)
 
     effect_registry = get_registry()
 
@@ -171,16 +171,21 @@ def run_pipeline_mode(preset_name: str = "demo"):
         from engine.pipeline.adapters import CameraStage
 
         camera = None
-        if preset.camera == "vertical":
-            camera = Camera.vertical()
+        speed = getattr(preset, "camera_speed", 1.0)
+        if preset.camera == "feed":
+            camera = Camera.feed(speed=speed)
+        elif preset.camera == "scroll":
+            camera = Camera.scroll(speed=speed)
+        elif preset.camera == "vertical":
+            camera = Camera.scroll(speed=speed)  # Backwards compat
         elif preset.camera == "horizontal":
-            camera = Camera.horizontal()
+            camera = Camera.horizontal(speed=speed)
         elif preset.camera == "omni":
-            camera = Camera.omni()
+            camera = Camera.omni(speed=speed)
         elif preset.camera == "floating":
-            camera = Camera.floating()
+            camera = Camera.floating(speed=speed)
         elif preset.camera == "bounce":
-            camera = Camera.bounce()
+            camera = Camera.bounce(speed=speed)
 
         if camera:
             pipeline.add_stage("camera", CameraStage(camera, name=preset.camera))
@@ -213,6 +218,7 @@ def run_pipeline_mode(preset_name: str = "demo"):
     ctx.set("items", items)
     ctx.set("pipeline", pipeline)
     ctx.set("pipeline_order", pipeline.execution_order)
+    ctx.set("camera_y", 0)
 
     current_width = 80
     current_height = 24