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/scripts/prune-backups.sh

@@ -0,0 +1,14 @@
+#!/bin/sh
+set -eu
+
+# Prune mc-proxy database backups older than RETAIN_DAYS (default 30).
+BACKUP_DIR="/srv/mc-proxy/backups"
+RETAIN_DAYS="${1:-30}"
+
+if [ ! -d "${BACKUP_DIR}" ]; then
+    echo "Backup directory ${BACKUP_DIR} does not exist."
+    exit 0
+fi
+
+find "${BACKUP_DIR}" -name "mc-proxy-*.db" -type f -mtime "+${RETAIN_DAYS}" -delete
+echo "Pruned backups older than ${RETAIN_DAYS} days from ${BACKUP_DIR}."