e2e: run health probe + Playwright on the compose network

Gitea's act-style runners execute workflow steps inside a runner
container, so compose's host port-publish (127.0.0.1:8080:8080) is
not reachable from the steps. PR #23's e2e job timed out waiting
for the server even though the container was up and listening.

Move both the health probe and the Playwright run onto rmnet so
they address the server as http://server:8080:

* health probe: docker run --rm --network e2e_rmnet curlimages/curl
* Playwright: new mcr.microsoft.com/playwright-based image, added
  as a profile-gated `playwright` service in compose.e2e.yml,
  invoked via `docker compose run --rm playwright`. Drops the
  setup-node + npm install runner steps.

.gitea/workflows/e2e.yml

@@ -1,12 +1,19 @@
 # P5-06 — End-to-end test suite.
 #
 # Spec : docs/superpowers/specs/2026-05-07-p5-oss-readiness-design.md
-# Stack: e2e/compose.e2e.yml (server + agent + rest-server)
+# Stack: e2e/compose.e2e.yml (server + agent + rest-server + playwright)
 # Tests: e2e/playwright/tests/*.spec.ts
 #
 # Triggered on every PR into main and on workflow_dispatch. Runs
 # longer than the unit-test workflow (~3-4 minutes for a clean run);
 # kept separate so a slow e2e doesn't block the fast lint/test loop.
+#
+# Networking note: every interaction with the server (health probe,
+# Playwright) happens from a container on the compose `rmnet`
+# network, addressing the server as `http://server:8080`. We can't
+# rely on `127.0.0.1:8080` because Gitea's runner executes steps
+# inside its own container, where compose's host port-publish is
+# not visible.
 
 name: e2e
 
@@ -33,7 +40,8 @@ jobs:
         run: |
           set -eu
           for i in $(seq 1 30); do
-            if curl -fsS http://127.0.0.1:8080/api/version >/dev/null 2>&1; then
+            if docker run --rm --network e2e_rmnet curlimages/curl:8.10.1 \
+                  -fsS http://server:8080/api/version >/dev/null 2>&1; then
               echo "server up"; exit 0
             fi
             sleep 2
@@ -60,22 +68,15 @@ jobs:
       - name: Start the agent
         run: docker compose -f e2e/compose.e2e.yml up -d agent
 
-      - uses: actions/setup-node@v4
-        with:
-          node-version: '20'
-
-      - name: Install Playwright
-        working-directory: e2e/playwright
+      - name: Prepare report mounts
         run: |
-          npm install --no-audit --no-fund
-          npx playwright install --with-deps chromium
+          mkdir -p e2e/playwright/playwright-report e2e/playwright/test-results
+          chmod -R a+rwX e2e/playwright/playwright-report e2e/playwright/test-results
 
       - name: Run Playwright tests
-        working-directory: e2e/playwright
         env:
-          RM_BASE_URL: http://127.0.0.1:8080
           RM_BOOTSTRAP_TOKEN: ${{ env.RM_BOOTSTRAP_TOKEN }}
-        run: npx playwright test
+        run: docker compose -f e2e/compose.e2e.yml run --rm playwright
 
       - name: Compose logs (on failure)
         if: failure()