CI time limit on the step; no timeout in Dockerfile or scripts (closes #199)

The runner ignores a job's timeout-minutes, so the 20-minute limit moves
to the step that runs script/cibuild. The Dockerfile frontend-test stage,
script/frontend-test and script/frontend-viewport-test drop their timeout
wrappers, which failed make check on a busy host. go test's -timeout 90s
stays, as REPO_POLICIES.md requires it.

Model: opus-5-5

script/frontend-test

@@ -15,13 +15,13 @@ ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 main() {
     cd "$ROOT"
     NODE_OPTIONS=--test-reporter=dot \
-        timeout 90 "$ROOT/script/yarn" --silent run test || {
+        "$ROOT/script/yarn" --silent run test || {
         echo "--- Rerunning with every test listed for details ---"
         NODE_OPTIONS=--test-reporter=spec \
-            timeout 90 "$ROOT/script/yarn" --silent run test
+            "$ROOT/script/yarn" --silent run test
         exit 1
     }
-    timeout 30 "$ROOT/script/yarn" build
+    "$ROOT/script/yarn" build
 }
 
 main "$@"