Phase 3: Behavior system with grid.step() turn manager

- Add EntityBehavior struct with 11 behavior types: IDLE, CUSTOM,
  NOISE4/8, PATH, WAYPOINT, PATROL, LOOP, SLEEP, SEEK, FLEE.
  Each returns BehaviorOutput (MOVED/DONE/BLOCKED/NO_ACTION) without
  modifying entity position directly (closes #300)
- Add grid.step(n=1, turn_order=None) turn manager: groups entities
  by turn_order, executes behaviors, fires triggers (TARGET/DONE/BLOCKED),
  updates cell_position and spatial hash. Snapshot-based iteration for
  callback safety (closes #301)
- Entity properties: behavior_type (read-only), turn_order, move_speed,
  target_label, sight_radius. Method: set_behavior(type, waypoints,
  turns, path)
- Update ColorLayer::updatePerspective to use cell_position

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/EntityBehavior.h

@@ -0,0 +1,81 @@
+#pragma once
+#include "Common.h"
+#include <vector>
+#include <string>
+#include <memory>
+
+// Forward declarations
+class UIEntity;
+class UIGrid;
+class DijkstraMap;
+
+// =============================================================================
+// BehaviorType - matches Python mcrfpy.Behavior enum values
+// =============================================================================
+enum class BehaviorType : int {
+    IDLE     = 0,
+    CUSTOM   = 1,
+    NOISE4   = 2,
+    NOISE8   = 3,
+    PATH     = 4,
+    WAYPOINT = 5,
+    PATROL   = 6,
+    LOOP     = 7,
+    SLEEP    = 8,
+    SEEK     = 9,
+    FLEE     = 10
+};
+
+// =============================================================================
+// BehaviorResult - outcome of a single behavior step
+// =============================================================================
+enum class BehaviorResult {
+    NO_ACTION,  // No movement attempted (IDLE, CUSTOM, etc.)
+    MOVED,      // Entity wants to move to target_cell
+    DONE,       // Behavior completed (path exhausted, sleep finished)
+    BLOCKED     // Movement blocked (wall or collision)
+};
+
+// =============================================================================
+// BehaviorOutput - result of executing a behavior
+// =============================================================================
+struct BehaviorOutput {
+    BehaviorResult result = BehaviorResult::NO_ACTION;
+    sf::Vector2i target_cell{0, 0};  // For MOVED/BLOCKED: the intended destination
+};
+
+// =============================================================================
+// EntityBehavior - behavior state attached to each entity
+// =============================================================================
+struct EntityBehavior {
+    BehaviorType type = BehaviorType::IDLE;
+
+    // Waypoint/path data
+    std::vector<sf::Vector2i> waypoints;
+    int current_waypoint_index = 0;
+    int patrol_direction = 1;  // +1 forward, -1 backward
+    std::vector<sf::Vector2i> current_path;
+    int path_step_index = 0;
+
+    // Sleep data
+    int sleep_turns_remaining = 0;
+
+    // Dijkstra map (for SEEK/FLEE)
+    std::shared_ptr<DijkstraMap> dijkstra_map;
+
+    void reset() {
+        type = BehaviorType::IDLE;
+        waypoints.clear();
+        current_waypoint_index = 0;
+        patrol_direction = 1;
+        current_path.clear();
+        path_step_index = 0;
+        sleep_turns_remaining = 0;
+        dijkstra_map = nullptr;
+    }
+};
+
+// =============================================================================
+// Behavior execution - does NOT modify entity position, just returns intent
+// =============================================================================
+BehaviorOutput executeBehavior(UIEntity& entity, UIGrid& grid);