Rename proto/gen directories from mc-proxy to mc_proxy for valid protobuf
package naming. Add CLI status subcommand for querying running instance
health via gRPC. Add systemd backup service/timer and backup pruning
script. Add buf.yaml and proto-lint Makefile target. Add shutdown_timeout
config field.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
