chore(e2e): add ESLint + Prettier; fix real findings; dedupe BASE

The Playwright suite had no linter and no formatter — only tsc. Add flat-config ESLint
(typescript-eslint, type-aware) and Prettier (2-space, matching the suite's style).

Rules keep the ones that catch real TEST bugs and drop the noise:
  - no-floating-promises KEPT — an un-awaited request/assertion can let a test end before it runs,
    passing vacuously. It caught one: the SSE reader loop in sse-listener is now explicitly `void`.
  - no-unused-vars KEPT — caught three dead bindings (an unused adminToken fixture arg, an unused
    `api` arg, an unused JPEG_MAGIC import), all removed.
  - no-explicit-any OFF — all test code; `any` is the honest type for an untyped res.json() body or
    a page.evaluate() return.
  - no-empty-pattern OFF — Playwright's dependency-free fixtures are `async ({}, use) => {}`.

Refactor: `const BASE = process.env.E2E_FRONTEND_URL ?? '...'` was redeclared verbatim in 23
files — extracted to helpers/env.ts and imported, so a port/scheme change is one edit not a sweep.

Then `prettier --write`. Verified: eslint clean, tsc clean, prettier clean, desktop suite 210
passed / 1 skipped. (One mobile spec flaked once under retries:0 — a pre-existing cross-test
reflow-timing vector from the flakiness audit, not this change: the each-key edit is stable across
16 isolated runs and a clean full mobile re-run.)

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

e2e/specs/03-feed/comment-ui.spec.ts

@@ -7,8 +7,7 @@
  */
 import { test, expect } from '../../fixtures/test';
 import { seedUpload } from '../../helpers/seed';
-
-const BASE = process.env.E2E_FRONTEND_URL ?? 'http://localhost:3101';
+import { BASE } from '../../helpers/env';
 
 test.describe('Comments — UI round-trip (CR1)', () => {
   test('a comment typed in the lightbox persists to the backend', async ({

e2e/specs/03-feed/like-comment.spec.ts

@@ -8,8 +8,7 @@
 import { test, expect } from '../../fixtures/test';
 import { SseListener } from '../../helpers/sse-listener';
 import { seedUpload, seedComment, findFeedRow } from '../../helpers/seed';
-
-const BASE = process.env.E2E_FRONTEND_URL ?? 'http://localhost:3101';
+import { BASE } from '../../helpers/env';
 
 async function like(jwt: string, uploadId: string): Promise<number> {
   const res = await fetch(`${BASE}/api/v1/upload/${uploadId}/like`, {
@@ -20,7 +19,10 @@ async function like(jwt: string, uploadId: string): Promise<number> {
 }
 
 test.describe('Feed — like + comment', () => {
-  test('a like counts once per user and toggles off on repeat (no double-count)', async ({ api, guest }) => {
+  test('a like counts once per user and toggles off on repeat (no double-count)', async ({
+    api,
+    guest,
+  }) => {
     const author = await guest('Author');
     const liker = await guest('Liker');
     const uploadId = await seedUpload(author.jwt);

e2e/specs/03-feed/sse-realtime.spec.ts

@@ -11,7 +11,11 @@ import { test, expect } from '../../fixtures/test';
 import { trackStreamOpens } from '../../helpers/sse';
 
 test.describe('Feed — SSE behavior', () => {
-  test('backgrounding then foregrounding the tab opens a fresh SSE connection', async ({ page, guest, signIn }) => {
+  test('backgrounding then foregrounding the tab opens a fresh SSE connection', async ({
+    page,
+    guest,
+    signIn,
+  }) => {
     const g = await guest('SseReconnect');
     const streamOpens = trackStreamOpens(page);
 
@@ -25,7 +29,10 @@ test.describe('Feed — SSE behavior', () => {
     // new stream opens while hidden.
     await page.evaluate(() => {
       Object.defineProperty(document, 'hidden', { configurable: true, get: () => true });
-      Object.defineProperty(document, 'visibilityState', { configurable: true, get: () => 'hidden' });
+      Object.defineProperty(document, 'visibilityState', {
+        configurable: true,
+        get: () => 'hidden',
+      });
       document.dispatchEvent(new Event('visibilitychange'));
     });
     // Snapshot the count AFTER backgrounding — this baselines out the initial open (and
@@ -36,7 +43,10 @@ test.describe('Feed — SSE behavior', () => {
     // Foreground again → connectSse() mints a new ticket and opens a new EventSource.
     await page.evaluate(() => {
       Object.defineProperty(document, 'hidden', { configurable: true, get: () => false });
-      Object.defineProperty(document, 'visibilityState', { configurable: true, get: () => 'visible' });
+      Object.defineProperty(document, 'visibilityState', {
+        configurable: true,
+        get: () => 'visible',
+      });
       document.dispatchEvent(new Event('visibilitychange'));
     });
 

e2e/specs/03-feed/toast-on-failure.spec.ts

@@ -33,7 +33,10 @@ test.describe('Feed — error toast on user action failures', () => {
       route.fulfill({
         status: 429,
         contentType: 'application/json',
-        body: JSON.stringify({ error: 'rate_limited', message: 'Zu viele Anfragen — bitte kurz warten.' }),
+        body: JSON.stringify({
+          error: 'rate_limited',
+          message: 'Zu viele Anfragen — bitte kurz warten.',
+        }),
       })
     );