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>

src/GridLayers.h

@@ -11,6 +11,7 @@
 // Forward declarations
 class UIGrid;
 class PyTexture;
+class UIEntity;
 
 // Include PyTexture.h for PyTextureObject (typedef, not struct)
 #include "PyTexture.h"
@@ -89,6 +90,13 @@ class ColorLayer : public GridLayer {
 public:
     std::vector<sf::Color> colors;
 
+    // Perspective binding (#113) - binds layer to entity for automatic FOV updates
+    std::weak_ptr<UIEntity> perspective_entity;
+    sf::Color perspective_visible;
+    sf::Color perspective_discovered;
+    sf::Color perspective_unknown;
+    bool has_perspective;
+
     ColorLayer(int z_index, int grid_x, int grid_y, UIGrid* parent);
 
     // Access color at position
@@ -109,6 +117,18 @@ public:
                  const sf::Color& discovered,
                  const sf::Color& unknown);
 
+    // Perspective binding (#113) - bind layer to entity for automatic updates
+    void applyPerspective(std::shared_ptr<UIEntity> entity,
+                          const sf::Color& visible,
+                          const sf::Color& discovered,
+                          const sf::Color& unknown);
+
+    // Update perspective - redraws based on bound entity's current position
+    void updatePerspective();
+
+    // Clear perspective binding
+    void clearPerspective();
+
     // Render a specific chunk to its texture (called when chunk is dirty AND visible)
     void renderChunkToTexture(int chunk_x, int chunk_y, int cell_width, int cell_height) override;
 
@@ -185,6 +205,9 @@ public:
     static PyObject* ColorLayer_fill(PyColorLayerObject* self, PyObject* args);
     static PyObject* ColorLayer_fill_rect(PyColorLayerObject* self, PyObject* args, PyObject* kwds);
     static PyObject* ColorLayer_draw_fov(PyColorLayerObject* self, PyObject* args, PyObject* kwds);
+    static PyObject* ColorLayer_apply_perspective(PyColorLayerObject* self, PyObject* args, PyObject* kwds);
+    static PyObject* ColorLayer_update_perspective(PyColorLayerObject* self, PyObject* args);
+    static PyObject* ColorLayer_clear_perspective(PyColorLayerObject* self, PyObject* args);
     static PyObject* ColorLayer_get_z_index(PyColorLayerObject* self, void* closure);
     static int ColorLayer_set_z_index(PyColorLayerObject* self, PyObject* value, void* closure);
     static PyObject* ColorLayer_get_visible(PyColorLayerObject* self, void* closure);