feat: add get_weather MCP tool using wttr.in API

- New agent/weather_mcp.py: stdio MCP server with get_weather(location)
  that returns a short conversational summary (temp, conditions, high/low)
- Register weather toolset in build_mcp_toolsets() alongside web-access
- Update system prompt with Weather section

agent/voice_agent.egg-info/requires.txt

@@ -0,0 +1,4 @@
+livekit-agents[mcp]~=1.7
+livekit-plugins-azure~=1.7
+livekit-plugins-openai~=1.7
+python-dotenv