docs: align architecture and API docs with Go 1.27 ingress support

- document HTTP/1.1, HTTP/2, and HTTP/3 ingress
- describe SSE streaming and timeout behavior
- document HTTP/2 and HTTP/3 Extended CONNECT
- update yamux stream and deployment architecture
- document Go 1.27 and UDP HTTP/3 requirements

internal/tunnel/types.go

@@ -6,12 +6,3 @@ import "context"
 type DomainValidator interface {
 	ValidateDomainAPIKey(ctx context.Context, domain, clientAPIKey string) error
 }
-
-// Response is the response returned by a tunnel transport to the public HTTP ingress.
-type Response struct {
-	RequestID string
-	Status    int
-	Header    map[string][]string
-	Body      []byte
-	Error     string
-}