Refactor MCP tools into modular directory structure

Split the monolithic tools.rs into separate files per tool:
- tools/mod.rs: Exports, dispatch, and shared helpers
- tools/create_weaver.rs: Create weaver tool
- tools/list_weavers.rs: List weavers tool
- tools/get_weaver.rs: Get weaver tool
- tools/delete_weaver.rs: Delete weaver tool
- tools/attach_weaver.rs: Attach weaver tool

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: ghuntley