feat: Add TurnOrchestrator for multi-turn LLM simulation (addresses #156)

TurnOrchestrator: Coordinates multi-agent turn-based simulation
- Perspective switching with FOV layer updates
- Screenshot capture per agent per turn
- Pluggable LLM query callback
- SimulationStep/SimulationLog for full context capture
- JSON save/load with replay support

New demos:
- 2_integrated_demo.py: WorldGraph + action execution integration
- 3_multi_turn_demo.py: Complete multi-turn simulation with logging

Updated 1_multi_agent_demo.py with action parser/executor integration.

Tested with Qwen2.5-VL-32B: agents successfully navigate based on
WorldGraph descriptions and VLM visual input.

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

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

tests/vllm_demo/1_multi_agent_demo.py

@@ -22,6 +22,9 @@ import base64
 import os
 import random
 
+from action_parser import parse_action
+from action_executor import ActionExecutor
+
 # VLLM configuration
 VLLM_URL = "http://192.168.1.100:8100/v1/chat/completions"
 SCREENSHOT_DIR = "/tmp/vllm_multi_agent"
@@ -284,6 +287,9 @@ def run_demo():
     # Setup scene
     grid, fov_layer, agents, rat = setup_scene()
 
+    # Create action executor
+    executor = ActionExecutor(grid)
+
     # Cycle through each agent's perspective
     for i, agent in enumerate(agents):
         print(f"\n{'='*70}")
@@ -319,6 +325,21 @@ def run_demo():
         print(f"\n{agent.name}'s Response:\n{response}")
         print()
 
+        # Parse and execute action
+        print(f"--- Action Execution ---")
+        action = parse_action(response)
+        print(f"Parsed action: {action.type.value} {action.args}")
+
+        result = executor.execute(agent, action)
+        if result.success:
+            print(f"SUCCESS: {result.message}")
+            if result.new_position:
+                # Update perspective after movement
+                switch_perspective(grid, fov_layer, agent)
+                mcrfpy.step(0.016)
+        else:
+            print(f"FAILED: {result.message}")
+
     print("\n" + "=" * 70)
     print("Multi-Agent Demo Complete")
     print("=" * 70)