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/camera.py

@@ -17,7 +17,8 @@ from enum import Enum, auto
 
 
 class CameraMode(Enum):
-    VERTICAL = auto()
+    FEED = auto()  # Single item view (static or rapid cycling)
+    SCROLL = auto()  # Smooth vertical scrolling (movie credits style)
     HORIZONTAL = auto()
     OMNI = auto()
     FLOATING = auto()
@@ -55,12 +56,14 @@ class Camera:
 
     x: int = 0
     y: int = 0
-    mode: CameraMode = CameraMode.VERTICAL
+    mode: CameraMode = CameraMode.FEED
     speed: float = 1.0
     zoom: float = 1.0
     canvas_width: int = 200  # Larger than viewport for scrolling
     canvas_height: int = 200
     custom_update: Callable[["Camera", float], None] | None = None
+    _x_float: float = field(default=0.0, repr=False)
+    _y_float: float = field(default=0.0, repr=False)
     _time: float = field(default=0.0, repr=False)
 
     @property
@@ -128,8 +131,10 @@ class Camera:
             self.custom_update(self, dt)
             return
 
-        if self.mode == CameraMode.VERTICAL:
-            self._update_vertical(dt)
+        if self.mode == CameraMode.FEED:
+            self._update_feed(dt)
+        elif self.mode == CameraMode.SCROLL:
+            self._update_scroll(dt)
         elif self.mode == CameraMode.HORIZONTAL:
             self._update_horizontal(dt)
         elif self.mode == CameraMode.OMNI:
@@ -159,9 +164,15 @@ class Camera:
         if vh < self.canvas_height:
             self.y = max(0, min(self.y, self.canvas_height - vh))
 
-    def _update_vertical(self, dt: float) -> None:
+    def _update_feed(self, dt: float) -> None:
+        """Feed mode: rapid scrolling (1 row per frame at speed=1.0)."""
         self.y += int(self.speed * dt * 60)
 
+    def _update_scroll(self, dt: float) -> None:
+        """Scroll mode: smooth vertical scrolling with float accumulation."""
+        self._y_float += self.speed * dt * 60
+        self.y = int(self._y_float)
+
     def _update_horizontal(self, dt: float) -> None:
         self.x += int(self.speed * dt * 60)
 
@@ -230,10 +241,86 @@ class Camera:
         self.canvas_height = height
         self._clamp_to_bounds()
 
+    def apply(
+        self, buffer: list[str], viewport_width: int, viewport_height: int | None = None
+    ) -> list[str]:
+        """Apply camera viewport to a text buffer.
+
+        Slices the buffer based on camera position (x, y) and viewport dimensions.
+        Handles ANSI escape codes correctly for colored/styled text.
+
+        Args:
+            buffer: List of strings representing lines of text
+            viewport_width: Width of the visible viewport in characters
+            viewport_height: Height of the visible viewport (overrides camera's viewport_height if provided)
+
+        Returns:
+            Sliced buffer containing only the visible lines and columns
+        """
+        from engine.effects.legacy import vis_offset, vis_trunc
+
+        if not buffer:
+            return buffer
+
+        # Get current viewport bounds (clamped to canvas size)
+        viewport = self.get_viewport()
+
+        # Use provided viewport_height if given, otherwise use camera's viewport
+        vh = viewport_height if viewport_height is not None else viewport.height
+
+        # Vertical slice: extract lines that fit in viewport height
+        start_y = viewport.y
+        end_y = min(viewport.y + vh, len(buffer))
+
+        if start_y >= len(buffer):
+            # Scrolled past end of buffer, return empty viewport
+            return [""] * vh
+
+        vertical_slice = buffer[start_y:end_y]
+
+        # Horizontal slice: apply horizontal offset and truncate to width
+        horizontal_slice = []
+        for line in vertical_slice:
+            # Apply horizontal offset (skip first x characters, handling ANSI)
+            offset_line = vis_offset(line, viewport.x)
+            # Truncate to viewport width (handling ANSI)
+            truncated_line = vis_trunc(offset_line, viewport_width)
+
+            # Pad line to full viewport width to prevent ghosting when panning
+            import re
+
+            visible_len = len(re.sub(r"\x1b\[[0-9;]*m", "", truncated_line))
+            if visible_len < viewport_width:
+                truncated_line += " " * (viewport_width - visible_len)
+
+            horizontal_slice.append(truncated_line)
+
+        # Pad with empty lines if needed to fill viewport height
+        while len(horizontal_slice) < vh:
+            horizontal_slice.append("")
+
+        return horizontal_slice
+
+    @classmethod
+    def feed(cls, speed: float = 1.0) -> "Camera":
+        """Create a feed camera (rapid single-item scrolling, 1 row/frame at speed=1.0)."""
+        return cls(mode=CameraMode.FEED, speed=speed, canvas_height=200)
+
+    @classmethod
+    def scroll(cls, speed: float = 0.5) -> "Camera":
+        """Create a smooth scrolling camera (movie credits style).
+
+        Uses float accumulation for sub-integer speeds.
+        Sets canvas_width=0 so it matches viewport_width for proper text wrapping.
+        """
+        return cls(
+            mode=CameraMode.SCROLL, speed=speed, canvas_width=0, canvas_height=200
+        )
+
     @classmethod
     def vertical(cls, speed: float = 1.0) -> "Camera":
-        """Create a vertical scrolling camera."""
-        return cls(mode=CameraMode.VERTICAL, speed=speed, canvas_height=200)
+        """Deprecated: Use feed() or scroll() instead."""
+        return cls(mode=CameraMode.FEED, speed=speed, canvas_height=200)
 
     @classmethod
     def horizontal(cls, speed: float = 1.0) -> "Camera":