make test-webkit runs the drag specs in WebKit against the test stack

WebKit takes *.localhost to loopback through GLib and ignores /etc/hosts, so
the container shares Traefik's network namespace. The webkit project only
exists with PLAYWRIGHT_WEBKIT=1, so test-frontend stays Chromium only.

Makefile

@@ -3,7 +3,7 @@
 # The workspace root delegates to these (see ../Makefile).
 
 .PHONY: init env-check dev-utils dev dev-local dev-lan rebuild-frontend up down update install dev-backend dev-frontend \
-        generate-client sync-example test test-backend test-checks test-stack test-frontend soak \
+        generate-client sync-example test test-backend test-checks test-stack test-frontend test-webkit soak \
         bench-startup lint lint-backend lint-frontend format-frontend umami build docs docs-serve clean help
 
 COMPOSE_ROOT := $(CURDIR)
@@ -225,6 +225,13 @@ test-frontend: test-stack  ## Run frontend tests (Playwright e2e) against the te
 	  -e HOST_RESOLVER_RULES="MAP app.$(TEST_DOMAIN) $$ip, MAP api.$(TEST_DOMAIN) $$ip" \
 	  $(PW_IMAGE) npx playwright test $(PLAYWRIGHT_ARGS)
 
+# WebKit takes *.localhost to loopback through GLib and ignores /etc/hosts, so
+# this run shares Traefik's network namespace, where loopback *is* Traefik.
+# Only the drag specs, which is where the engines differ.
+test-webkit: test-stack  ## Run the drag specs in WebKit against the test stack
+	@$(PW_RUN) --network container:fluksio-app-proxy-1 -e PLAYWRIGHT_WEBKIT=1 \
+	  $(PW_IMAGE) npx playwright test --project=webkit $(PLAYWRIGHT_ARGS)
+
 # Load and chaos against a *running* stack, never part of `make test`: it
 # restarts this stack's containers. `SOAK_ARGS="--dry-run"` only looks.
 soak:  ## Run the soak/chaos harness (SOAK_ARGS="--minutes 30 --scenario redis --force")