test(e2e): address self-review follow-ups (dedup, XSS render guard, SSE hardening)

Follow-ups from the code review of the test-quality batches:

- Consolidate duplicated helpers into e2e/helpers/: seed.ts (seedUpload,
  seedComment, listComments, findFeedRow) and sse.ts (mintSseTicket, openStream,
  trackStreamOpens). Refactor authorization-deep, xss-injection, like-comment,
  sse-ticket-abuse, ddos, sse-realtime, multi-tab, and SseListener to use them —
  the upload/comment/ticket-flow contracts now live in one place each instead of
  being re-inlined across 3–7 specs.
- xss-injection display-name loop: it navigated to /feed (which renders uploader
  names, not the viewer's) so "nothing fired" passed vacuously — the payload was
  never rendered. Now navigate to /account (the actual sink) and add a render
  guard asserting the payload reached the DOM as escaped text before checking
  __xssFired.
- sse-realtime reconnect: snapshot the stream-open count AFTER backgrounding, so
  the "new connection" assertion is attributable to the foreground event and can't
  be satisfied by a spurious native/error reconnect before the toggle.
- recover-page: correct the comment (auto-submit is the onPinInput handler, not an
  $effect).

44 affected specs verified green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

e2e/specs/07-adversarial/ddos.spec.ts

@@ -4,6 +4,7 @@
  * or rejected gracefully without crashing the backend.
  */
 import { test, expect } from '../../fixtures/test';
+import { mintSseTicket } from '../../helpers/sse';
 
 const BASE = process.env.E2E_FRONTEND_URL ?? 'http://localhost:3101';
 
@@ -48,15 +49,9 @@ test.describe('Adversarial — small-scale abuse', () => {
     const g = await guest('SseFlood');
     // The stream endpoint authenticates via single-use tickets (POST /stream/ticket),
     // not the raw JWT — a `?token=` open is rejected with 400. Mint one ticket per stream.
-    const mintTicket = async () => {
-      const res = await fetch(`${BASE}/api/v1/stream/ticket`, {
-        method: 'POST',
-        headers: { Authorization: `Bearer ${g.jwt}` },
-      });
-      const json: any = await res.json();
-      return json.ticket as string;
-    };
-    const tickets = await Promise.all(Array.from({ length: 10 }, mintTicket));
+    // (These streams must be held open concurrently, so we can't use the openStream
+    // helper which opens-and-aborts a single stream.)
+    const tickets = await Promise.all(Array.from({ length: 10 }, () => mintSseTicket(g.jwt)));
 
     const controllers = tickets.map(() => new AbortController());
     const requests = tickets.map((ticket, i) =>