Add multi-agent coordination and benchmark papers

[zfw1226]

Summary

This PR adds four multi-agent coordination, benchmark, and reinforcement learning papers across the most relevant existing sections.

Added papers

• Multi-Agent Collaboration and System Design
  • ToM2C: Target-oriented Multi-agent Communication and Cooperation with Theory of Mind
• Multi-Agent Frameworks and Benchmarks
  • MATE: Benchmarking Multi-Agent Reinforcement Learning in Distributed Target Coverage Control
• Application-Specific Multi-Agent Systems / Multimodal
  • Proactive Multi-Camera Collaboration for 3D Human Pose Estimation
• Reinforcement Learning
  • Learning Multi-Agent Coordination for Enhancing Target Coverage in Directional Sensor Networks

Rationale

These papers cover multi-agent communication, cooperation, coordination benchmarks, multimodal multi-camera collaboration, and MARL-based target coverage control, matching the repository's broader multi-agent systems scope.