Tool registry with hot-reload support

[souvikghosh04]

1. Create McpToolRegistry service (singleton)
2. Subscribe to RuntimeConfigProvider config change events
3. Rebuild tools when config changes
4. Tools always fresh, metadata always accurate

this is only an attempt to reduce staleness of metadata of MCP tools. however, the general recommendation would be perform a clean start for any config changes. this is more robust and environment agnostic.