Add lifecycle management for beads-mcp processes (bd-148)

- Register atexit handler to close daemon connections
- Add signal handlers for SIGTERM/SIGINT for graceful shutdown
- Implement cleanup() to close all daemon client connections
- Track daemon clients globally for cleanup
- Add close() method to BdDaemonClient (no-op since connections are per-request)
- Register client on first use via _get_client()
- Add comprehensive lifecycle tests

This prevents MCP server processes from accumulating without cleanup.
Each tool invocation will now properly clean up on exit.

Amp-Thread-ID: https://ampcode.com/threads/T-05d76b8e-dac9-472b-bfd0-afe10e3457cd
Co-authored-by: Amp <amp@ampcode.com>

integrations/beads-mcp/uv.lock

@@ -48,7 +48,7 @@ wheels = [
 
 [[package]]
 name = "beads-mcp"
-version = "0.9.9"
+version = "0.9.10"
 source = { editable = "." }
 dependencies = [
     { name = "fastmcp" },