Skip live network feed test under -short for deterministic make check (closes #2)

TestRouteWatchLiveFeed streams the live RIPE RIS feed for about five
seconds, which made make check nondeterministic and network-dependent.
Guard it with a testing.Short() skip and pass -short in both go test
lines of script/test, so the default suite runs offline and
deterministically. The README documents how to run the live test on
demand.

Test-only change; no production behavior changes.

Model: opus-4-8

script/test

@@ -7,9 +7,9 @@ ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
-    go test -timeout 30s -race -cover ./... || {
+    go test -short -timeout 30s -race -cover ./... || {
         echo "--- Rerunning with -v for details ---"
-        go test -timeout 30s -race -v ./...
+        go test -short -timeout 30s -race -v ./...
         exit 1
     }
 }