feat: Add ColorLayer perspective methods and patrol demo (addresses #113)

ColorLayer enhancements:
- fill_rect(x, y, w, h, color): Fill rectangular region
- draw_fov(source, radius, fov, visible, discovered, unknown): One-time FOV draw
- apply_perspective(entity, visible, discovered, unknown): Bind layer to entity
- update_perspective(): Refresh layer from bound entity's gridstate
- clear_perspective(): Remove entity binding

New demo: tests/demo/perspective_patrol_demo.py
- Entity patrols around 10x10 central obstacle
- FOV layer shows visible/discovered/unknown states
- [R] to reset vision, [Space] to pause, [Q] to quit
- Demonstrates fog of war memory system

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

tests/demo/perspective_patrol_demo.py

@@ -0,0 +1,204 @@
+#!/usr/bin/env python3
+"""
+Perspective Patrol Demo
+=======================
+
+Demonstrates the FOV/perspective system with an animated patrolling entity.
+
+Features:
+- 20x20 grid with 10x10 opaque obstacle in center
+- Entity patrols around the obstacle in a square pattern
+- ColorLayer shows fog of war (visible/discovered/unknown)
+- Press 'R' to reset vision (shows unknown vs discovered difference)
+- Press 'Space' to pause/resume patrol
+"""
+
+import mcrfpy
+
+# Patrol waypoints (clockwise around the center obstacle)
+WAYPOINTS = [
+    (3, 3),    # Top-left
+    (16, 3),   # Top-right
+    (16, 16),  # Bottom-right
+    (3, 16),   # Bottom-left
+]
+
+# State
+current_waypoint = 0
+patrol_paused = False
+move_timer_ms = 150  # Time between moves
+
+# Global references
+g_grid = None
+g_patrol = None
+g_fov_layer = None
+
+def setup_scene():
+    """Create the demo scene"""
+    global g_grid, g_patrol, g_fov_layer
+
+    mcrfpy.createScene("patrol_demo")
+    mcrfpy.setScene("patrol_demo")
+
+    ui = mcrfpy.sceneUI("patrol_demo")
+
+    # Title
+    title = mcrfpy.Caption(text="Perspective Patrol Demo", pos=(10, 10))
+    title.fill_color = mcrfpy.Color(255, 255, 255)
+    ui.append(title)
+
+    # Instructions
+    instructions = mcrfpy.Caption(text="[R] Reset vision  [Space] Pause/Resume  [Q] Quit", pos=(10, 35))
+    instructions.fill_color = mcrfpy.Color(180, 180, 180)
+    ui.append(instructions)
+
+    # Create grid (20x20, each cell 24px) - centered in 1024x768 window
+    grid_size_px = 480
+    grid = mcrfpy.Grid(
+        pos=((1024 - grid_size_px) // 2, (768 - grid_size_px) // 2),
+        size=(grid_size_px, grid_size_px),
+        grid_size=(20, 20),
+        texture=None
+    )
+    grid.center = (10*16, 10*16)
+    grid.fill_color = mcrfpy.Color(40, 40, 50)  # Dark floor background
+    ui.append(grid)
+
+    # Set FOV settings
+    grid.fov = mcrfpy.FOV.SHADOW
+    grid.fov_radius = 8
+
+    # Initialize all cells as walkable/transparent (floor)
+    for y in range(20):
+        for x in range(20):
+            point = grid.at(x, y)
+            point.walkable = True
+            point.transparent = True
+
+    # Create 10x10 obstacle box in center (cells 5-14 in both dimensions)
+    for y in range(5, 15):
+        for x in range(5, 15):
+            point = grid.at(x, y)
+            point.walkable = False
+            point.transparent = False
+
+    # Create a color layer for the walls (so we can see them)
+    wall_layer = grid.add_layer('color', z_index=-2)
+    wall_layer.fill((40, 40, 50, 255))  # Match floor color
+
+    # Draw walls on the wall layer
+    for y in range(5, 15):
+        for x in range(5, 15):
+            wall_layer.set(x, y, mcrfpy.Color(100, 70, 50, 255))  # Brown walls
+
+    # Create FOV layer (above walls, below entities)
+    fov_layer = grid.add_layer('color', z_index=-1)
+    fov_layer.fill((0, 0, 0, 255))  # Start completely black (unknown)
+
+    # Create patrolling entity
+    patrol = mcrfpy.Entity(WAYPOINTS[0])
+    patrol.sprite_index = 64  # '@' character typically
+    grid.entities.append(patrol)
+
+    # Bind FOV layer to entity
+    fov_layer.apply_perspective(
+        entity=patrol,
+        visible=(0, 0, 0, 0),              # Fully transparent when visible
+        discovered=(20, 20, 40, 180),       # Dark blue-gray when discovered
+        unknown=(0, 0, 0, 255)              # Black when never seen
+    )
+
+    # Initial visibility update
+    patrol.update_visibility()
+
+    # Store references for timer callbacks
+    g_grid = grid
+    g_patrol = patrol
+    g_fov_layer = fov_layer
+
+    # Status caption (below centered grid)
+    status = mcrfpy.Caption(text="Status: Patrolling", pos=(10, 720))
+    status.fill_color = mcrfpy.Color(100, 255, 100)
+    status.name = "status"
+    ui.append(status)
+
+    # Set up keyboard handler
+    mcrfpy.keypressScene(on_keypress)
+
+    # Start patrol timer
+    mcrfpy.setTimer("patrol", patrol_step, move_timer_ms)
+
+def patrol_step(runtime):
+    """Move entity one step toward current waypoint"""
+    global current_waypoint, patrol_paused
+
+    if patrol_paused:
+        return
+
+    # Get current position and target
+    px, py = int(g_patrol.x), int(g_patrol.y)
+    tx, ty = WAYPOINTS[current_waypoint]
+
+    # Calculate direction
+    dx = 0 if tx == px else (1 if tx > px else -1)
+    dy = 0 if ty == py else (1 if ty > py else -1)
+
+    # Move one step (prefer horizontal, then vertical)
+    if dx != 0:
+        g_patrol.x = px + dx
+    elif dy != 0:
+        g_patrol.y = py + dy
+
+    # Update visibility after move
+    g_patrol.update_visibility()
+
+    # Check if reached waypoint
+    if int(g_patrol.x) == tx and int(g_patrol.y) == ty:
+        current_waypoint = (current_waypoint + 1) % len(WAYPOINTS)
+        update_status(f"Reached waypoint, heading to {WAYPOINTS[current_waypoint]}")
+
+def on_keypress(key, state):
+    """Handle keyboard input"""
+    global patrol_paused
+
+    if state != "start":
+        return
+
+    if key == "R":
+        reset_vision()
+    elif key == "Space":
+        patrol_paused = not patrol_paused
+        if patrol_paused:
+            update_status("Status: PAUSED")
+        else:
+            update_status("Status: Patrolling")
+    elif key == "Q":
+        mcrfpy.setScene(None)
+
+def reset_vision():
+    """Reset entity's discovered state to demonstrate unknown vs discovered"""
+    global g_patrol, g_fov_layer
+
+    # Clear entity's gridstate (forget everything)
+    for state in g_patrol.gridstate:
+        state.visible = False
+        state.discovered = False
+
+    # Re-fill the layer with unknown color
+    g_fov_layer.fill((0, 0, 0, 255))
+
+    # Update visibility from current position (will mark current FOV as visible)
+    g_patrol.update_visibility()
+
+    update_status("Vision RESET - watch discovered vs unknown!")
+
+def update_status(text):
+    """Update status caption"""
+    ui = mcrfpy.sceneUI("patrol_demo")
+    for element in ui:
+        if hasattr(element, 'name') and element.name == "status":
+            element.text = text
+            break
+
+# Run the demo
+setup_scene()