Add opencode.json workspace configuration

[xnoto]

Summary

• adds workspace OpenCode configuration for this repository with the MCP servers used in local development and review flows
• adds a route-specific chatty throttle that delays bursty sender-to-agent-thread traffic while preserving ordering and isolating cooldowns per route
• adds throttle metrics plus targeted tests for helper logic, worker delivery timing, dropped-agent routing, session-agent behavior, and daemon integration

Testing

• uv run pytest tests/test_chatty_throttle.py -q
• uv run pytest tests/test_chatty_throttle.py tests/test_session_agents.py tests/test_model_routing.py tests/test_daemon_integration.py -q