Add per-route details to status, move socket to /srv/mc-proxy/

mcproxyctl status now shows individual routes per listener with
hostname, backend, mode, and re-encrypt indicator. Proto, gRPC
server, client library, and CLI all updated.

Default gRPC socket path moved from /var/run/mc-proxy.sock to
/srv/mc-proxy/mc-proxy.sock to match the service data directory
convention.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

internal/config/config.go

@@ -39,7 +39,7 @@ type Database struct {
 
 // GRPC holds the gRPC admin API configuration.
 type GRPC struct {
-	Addr string `toml:"addr"` // Unix socket path (e.g., "/var/run/mc-proxy.sock")
+	Addr string `toml:"addr"` // Unix socket path (e.g., "/srv/mc-proxy/mc-proxy.sock")
 }
 
 // Listener is a proxy listener with its routes.
@@ -218,7 +218,7 @@ func (c *Config) validate() error {
 	if c.GRPC.Addr != "" {
 		socketPath := c.GRPC.SocketPath()
 		if !strings.Contains(socketPath, "/") {
-			return fmt.Errorf("grpc.addr must be a Unix socket path (e.g., /var/run/mc-proxy.sock)")
+			return fmt.Errorf("grpc.addr must be a Unix socket path (e.g., /srv/mc-proxy/mc-proxy.sock)")
 		}
 	}