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>

internal/config/config.go

@@ -25,7 +25,8 @@ type GRPC struct {
 	Addr     string `toml:"addr"`
 	TLSCert  string `toml:"tls_cert"`
 	TLSKey   string `toml:"tls_key"`
-	ClientCA string `toml:"client_ca"`
+	CACert   string `toml:"ca_cert"`   // CA cert for verifying the server (client-side)
+	ClientCA string `toml:"client_ca"` // CA cert for verifying clients (server-side mTLS)
 }
 
 type Listener struct {