feat: Add WebSocket RCON client to companion agent

Wire gorilla/websocket into the Go companion agent to send arbitrary
console commands (e.g. oxide.reload BetterLoot) to the Rust Dedicated
Server's WebRCON endpoint. Adds RCON_PORT and RCON_PASSWORD env vars,
a new "command" action on the existing cmd.server NATS subject, and
the internal/rcon package that handles the JSON-over-WebSocket protocol.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

companion-agent/cmd/agent/main.go

@@ -31,6 +31,10 @@ type Config struct {
 	// Install directory for deployment
 	InstallDir string `envconfig:"INSTALL_DIR" default:""`
 
+	// RCON configuration
+	RconPort     int    `envconfig:"RCON_PORT" default:"28016"`
+	RconPassword string `envconfig:"RCON_PASSWORD" default:""`
+
 	// Optional settings
 	HeartbeatInterval int `envconfig:"HEARTBEAT_INTERVAL" default:"60"`
 	LogLevel          string `envconfig:"LOG_LEVEL" default:"info"`
@@ -63,6 +67,7 @@ func main() {
 	log.Printf("  Game Server Path: %s", cfg.GameServerPath)
 	log.Printf("  SteamCMD Path: %s", cfg.SteamCMDPath)
 	log.Printf("  Install Dir: %s", cfg.InstallDir)
+	log.Printf("  RCON Port: %d", cfg.RconPort)
 	log.Printf("  Heartbeat Interval: %ds", cfg.HeartbeatInterval)
 
 	// Create context with signal handling for graceful shutdown
@@ -88,6 +93,8 @@ func main() {
 		GameServerArgs:    cfg.GameServerArgs,
 		Version:           version,
 		InstallDir:        cfg.InstallDir,
+		RconPort:          cfg.RconPort,
+		RconPassword:      cfg.RconPassword,
 	}
 
 	// Start daemon