fix(ci): fix lint errors and pin CI to Go 1.25

- Run gofmt on all files
- Export SetupUPnP to fix unused lint error
- Remove Go 1.26 from CI matrix (only test with 1.25)

.github/workflows/ci.yml

@@ -15,7 +15,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        go-version: ["1.25", "1.26"]
+        go-version: ["1.25"]
     steps:
       - uses: actions/checkout@v6
 

internal/engine/upnp.go

@@ -17,9 +17,9 @@ type UPnPMapping struct {
 	device       upnp.Device
 }
 
-// setupUPnP discovers the gateway, maps the port, and gets the public IP.
+// SetupUPnP discovers the gateway, maps the port, and gets the public IP.
 // Returns nil if UPnP is not available or fails.
-func setupUPnP(internalPort int) (*UPnPMapping, error) {
+func SetupUPnP(internalPort int) (*UPnPMapping, error) {
 	log.Println("stream: discovering UPnP gateway (10s timeout)...")
 	devices := upnp.Discover(0, 10*time.Second, alog.Logger{})
 	if len(devices) == 0 {