Move all tool definitions and dispatch out of mcp-server.rs:
- Channel tools: new tools/channels.rs with definitions, async
dispatch, blocking dispatch, and capnp RPC helpers
- Memory tools: make tools/memory.rs pub so mcp-server can use it
mcp-server.rs is now pure JSON-RPC protocol plumbing (482 → 169 lines).
No tool-specific code remains in that file.
Also removes duplicated channel RPC helpers and fetch_all_channels
that were in both mcp-server.rs and thalamus/channels.rs.
Co-Authored-By: Proof of Concept <poc@bcachefs.org>
