Header limit of 32 KiB, upstream URL checks, build and run scripts

The request line and headers are now refused above 32 KiB exactly: Go's
server reads 4 KiB past MaxHeaderBytes, so that is set to 28 KiB, and
the tests try exactly 32 KiB and one byte more. SWWAF_UPSTREAM_URL now
needs a host, and a given port must be from 1 to 65535. make build and
make run call script/build and script/run.

Model: opus-5-5

internal/config/config_test.go

@@ -142,6 +142,9 @@ func TestInvalidValueStopsTheStart(t *testing.T) {
 		{upstreamURL, "127.0.0.1:8081"},
 		{upstreamURL, "ftp://127.0.0.1:8081"},
 		{upstreamURL, "http://"},
+		{upstreamURL, "http://:8081"},
+		{upstreamURL, "http://127.0.0.1:0"},
+		{upstreamURL, "http://127.0.0.1:99999"},
 		{upstreamURL, "http://127.0.0.1:8081/app"},
 		{upstreamURL, "http://127.0.0.1:8081/?a=1"},
 		{upstreamURL, "http://user:secret@127.0.0.1:8081"},