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

playwright.config.ts

@@ -25,7 +25,16 @@ export default defineConfig({
     trace: 'retain-on-failure',
     ...devices['Desktop Chrome'],
   },
-  projects: [{ name: 'chromium', use: { ...devices['Desktop Chrome'] } }],
+  projects: [
+    { name: 'chromium', use: { ...devices['Desktop Chrome'] } },
+    // [Gitea #221] WebKit as the Safari/iOS proxy. It runs the subset tagged
+    // @webkit / @ios (boot, composer round-trip, thread panel, lightbox): it
+    // catches WebKit-only breakage (CSS, dvh, IndexedDB, media decode) that
+    // Chromium emulation can't, but does not emulate the iOS keyboard or the
+    // Home-Screen install flow.
+    { name: 'webkit', use: { ...devices['Desktop Safari'] }, grep: /@webkit/ },
+    { name: 'iphone', use: { ...devices['iPhone 14'] }, grep: /@ios/ },
+  ],
   webServer: {
     command: `npx vite preview --port ${PORT} --strictPort`,
     url: BASE_URL,