ci(ui-test): clean root-owned build artifacts so runner teardown succeeds

In host-mode the ui-test job runs as root, so vite (test:pwa),
svelte-kit and Playwright write build/, .svelte-kit/, test-results/ and
playwright-report/ root-owned into the shared host workspace. The
act_runner (non-root) then cannot remove them at teardown
("unlinkat ui/frontend/build: permission denied"), which spuriously
marks this or a sibling job that inherits the dirty workspace as failed
— it hit go-unit on the #83 merge even though every test passed.

Add an `if: always()` step that removes those generated dirs while the
job still has root, after the artifact uploads. Keeps the shared
workspace clean for the runner's own teardown and for later jobs.

.gitea/workflows/ui-test.yaml

@@ -119,3 +119,16 @@ jobs:
           name: playwright-traces
           path: ui/frontend/test-results/
           retention-days: 14
+
+      - name: Remove root-owned build artifacts
+        if: always()
+        # In host-mode the job runs as root, so vite (test:pwa),
+        # svelte-kit and Playwright write these outputs root-owned into
+        # the shared host workspace. The act_runner (non-root) then
+        # cannot remove them at teardown ("unlinkat ... permission
+        # denied"), which spuriously fails this or a sibling job that
+        # inherits the dirty workspace (observed on go-unit). Clean them
+        # here while the step still has root, after the uploads above.
+        run: |
+          rm -rf ui/frontend/build ui/frontend/.svelte-kit \
+                 ui/frontend/test-results ui/frontend/playwright-report