refactor: unify agent communication with Transport interface

- Introduce `Transport` interface to abstract WebSocket and SSH
communication
- Add generic `Data` field to `AgentResponse` for streamlined future
endpoints
- Maintain backward compatibility with legacy hubs and agents using
typed fields
- Unify fetch operations (SMART, systemd, containers) under a single
`request` method
- Improve `RequestManager` with deadline awareness and legacy response
support
- Refactor agent response routing into dedicated `agent/response.go`
- Update version to 0.18.0-beta.2

internal/site/package.json

@@ -1,7 +1,7 @@
 {
 	"name": "beszel",
 	"private": true,
-	"version": "0.18.0-beta.1",
+	"version": "0.18.0-beta.2",
 	"type": "module",
 	"scripts": {
 		"dev": "vite --host",