ci(e2e): run the tagged specs under WebKit as the Safari/iOS proxy (#221)

Two new Playwright projects — 'webkit' (Desktop Safari) for tests tagged
@webkit and 'iphone' (iPhone 14 descriptor) for @ios — covering boot,
login + send/receive, the thread panel and the gallery lightbox. The CI
e2e job installs webkit next to chromium.

WebKit reports handled fetch failures (well-known probes, a wasm fetch cut
short by our own navigation) as page errors with its own wording, so the
benign allowlist now applies to page errors as well.

Locally: 8/8 green twice in a row against the local Synapse.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

.gitea/workflows/ci.yml

@@ -275,8 +275,11 @@ jobs:
             sleep $((attempt * 15))
           done
 
-      - name: Install Playwright Chromium
-        run: npx playwright install --with-deps chromium
+      # [Gitea #221] WebKit too — Playwright's Safari/iOS proxy for the tagged
+      # subset (see playwright.config.ts projects). `--with-deps` pulls the
+      # GTK/GStreamer libraries WebKit needs on the runner.
+      - name: Install Playwright browsers
+        run: npx playwright install --with-deps chromium webkit
 
       - name: Build
         run: npm run build