Add status command, deployment infrastructure, and fix proto paths

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>

deploy/systemd/mc-proxy-backup.timer

@@ -0,0 +1,10 @@
+[Unit]
+Description=Daily mc-proxy database backup
+
+[Timer]
+OnCalendar=*-*-* 02:00:00 UTC
+RandomizedDelaySec=300
+Persistent=true
+
+[Install]
+WantedBy=timers.target