feat(e2e): Playwright suite — 134 tests across 9 spec areas + UA matrix

Adds an end-to-end Playwright test suite under e2e/ that spins up an
isolated docker-compose stack (Postgres :55432, Caddy :3101, backend with
EVENTSNAP_TEST_MODE=1, SvelteKit adapter-node frontend) and exercises the
SvelteKit app against the real Rust backend.

Phase 1 — happy paths covering every documented USER_JOURNEYS.md flow:
  01-auth/      join, recover, admin login, leave event, PIN lockout
  02-upload/    gallery picker (API path), rate-limit + admin toggle
  03-feed/      like/comment SSE, filters, SSE reconnect on visibility
  04-host/      event lock API, ban/unban, promote
  05-admin/     config validation, foundational authz guards, stats
  06-export/    /export status + download stub
  __smoke/      cross-UA happy-path (runs on every UA project)

Phase 2 — adversarial + browser chaos:
  07-adversarial/  XSS payloads (6 × display name path), SQLi shapes,
                   length / encoding / RTL override / NUL byte;
                   file-upload boundaries (ELF body claimed as JPEG,
                   oversize vs max_image_size_mb, zero-byte, NUL
                   filename, path-traversal, SVG-with-script);
                   JWT alg:none, signature/payload tamper, expired
                   session, PIN brute-force (serial + parallel),
                   admin password brute-force; deep authz (cross-user
                   delete, banned user across like/comment/feed-read,
                   host→admin escalation); small-scale DDoS (20× /join,
                   10MB comment body, 10 concurrent SSE).
  08-browser-chaos/ localStorage / sessionStorage / cookie purge,
                    IndexedDB drop mid-session, offline → reconnect,
                    slow-3G, 503 flakes, 429 with no retry storm,
                    multi-tab same/different user, no-JS, hostile CSS,
                    clock skew ±1h / -2d, localStorage quota exhausted.

Phase 3 — mobile gestures (runs only on chromium-mobile / Pixel 7):
  09-mobile/    touch-target ≥44px audit, env(safe-area-inset-bottom)
                structural check, long-press (FeedListCard → ContextSheet,
                quick-tap negation, click-suppression), double-tap
                (feed card like + lightbox heart-burst, via synthetic
                pointer events to bypass the first-tap-fires-click trap),
                viewport reflow (portrait/landscape/narrow/phablet),
                plus fixme stubs documenting planned gestures (swipe
                lightbox L/R, swipe-down dismiss, pull-to-refresh,
                long-press-comment).

Cross-UA matrix (chromium-engine projects run @smoke only):
  chromium-pixel7, chromium-galaxy-s22, samsung-internet (Samsung UA
  emulation on Galaxy viewport), edge-android, plus webkit-iphone,
  chrome-ios, firefox-android, firefox-desktop — the latter four need
  libavif16 on the host (Playwright dep) but the configs are in place.

Infrastructure:
  - fixtures/test.ts central test.extend (api, db, adminToken, guest,
    host, signIn). Per-test DB truncate via the dev-only POST
    /admin/__truncate route, gated by EVENTSNAP_TEST_MODE=1.
  - helpers/sse-listener.ts, helpers/upload-client.ts (Node-side
    multipart for adversarial file-upload tests + JPEG/PNG/ELF magic
    constants), helpers/touch.ts (longPress / doubleTap / swipe /
    inlineStyle / computedStyle).
  - 10 page objects covering every route + UploadSheet/Lightbox.
  - global-setup waits for /health, logs in admin, disables every
    rate-limit and quota toggle.
  - .github/workflows/e2e.yml: PR check runs chromium-desktop + the
    smoke matrix in parallel, uploads playwright-report/ and traces on
    failure.

Findings the suite surfaces as live `[finding]` warnings (not silenced):
  1. /admin/login has no rate-limit or lockout (bcrypt cost only).
  2. PIN-attempt counter races under parallel /recover requests.
  3. Zero-byte uploads pass /api/v1/upload.
  4. SVG-with-script can pass the magic-byte check (consider CSP +
     X-Content-Type-Options on /media/*).

Stack-internal docs live in e2e/README.md (UA tier table, Samsung
Internet escalation tiers A/B/C, debugging tips, roadmap).

Final tally: 134 passed / 0 failed / 9 skipped (test.fixme stubs for
not-yet-shipped gestures and one UI-upload-flow investigation).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

e2e/specs/09-mobile/gestures-doubletap.spec.ts

@@ -0,0 +1,98 @@
+/**
+ * Phase 3 mobile — double-tap gesture.
+ *
+ * The `doubletap` action is wired in two places:
+ *
+ *   1. FeedListCard's image button — fires `ondoubletap` → onlike(upload.id).
+ *      Two rapid taps record a like. The on-screen like count increments
+ *      optimistically and is reconciled by an SSE `like-update`.
+ *
+ *   2. LightboxModal's media wrapper — fires the heart-burst animation
+ *      and calls onlike(). The animation is gated by the `heartBurst`
+ *      state which the spec asserts indirectly by observing the like count
+ *      increase.
+ */
+import { test, expect } from '../../fixtures/test';
+import { uploadRaw } from '../../helpers/upload-client';
+import { doubleTap } from '../../helpers/touch';
+import { readFileSync } from 'node:fs';
+import { join } from 'node:path';
+
+const SAMPLE_JPG = join(process.cwd(), 'fixtures', 'media', 'sample.jpg');
+
+async function seedUpload(token: string, caption = 'Doubletap fixture'): Promise<{ id: string }> {
+  const res = await uploadRaw(token, readFileSync(SAMPLE_JPG), {
+    filename: 'dt.jpg',
+    contentType: 'image/jpeg',
+    caption,
+  });
+  if (res.status !== 201) throw new Error(`Upload seed failed (${res.status}): ${await res.text()}`);
+  return (await res.json()) as { id: string };
+}
+
+test.describe('Mobile — double-tap gesture', () => {
+  test('double-tap on a feed card image button registers a like', async ({ api, page, guest, signIn }) => {
+    const author = await guest('DtAuthor');
+    const liker = await guest('DtLiker');
+    const { id: uploadId } = await seedUpload(author.jwt, 'Double-tap me');
+
+    await signIn(page, liker);
+    await page.goto('/feed');
+
+    // Locate the image button inside the card. The aria-label is "Bild vergrößern".
+    const imageButton = page.locator('article')
+      .filter({ hasText: author.displayName })
+      .first()
+      .getByRole('button', { name: 'Bild vergrößern' });
+    await expect(imageButton).toBeVisible({ timeout: 10_000 });
+
+    await doubleTap(page, imageButton);
+
+    // Wait for the optimistic increment OR the SSE-confirmed count. We assert via the
+    // API to avoid coupling to specific DOM markup for the like badge.
+    await expect.poll(async () => {
+      const feed = await api.getFeed(liker.jwt);
+      // Backend returns { uploads: [...], next_cursor }.
+      const list: any[] = feed.uploads ?? feed.items ?? feed;
+      const row = Array.isArray(list) ? list.find((u: any) => u.id === uploadId) : undefined;
+      return row?.like_count ?? row?.likes ?? 0;
+    }, { timeout: 5_000 }).toBeGreaterThanOrEqual(1);
+  });
+
+  test('double-tap inside the lightbox triggers the heart-burst (like recorded)', async ({ api, page, guest, signIn }) => {
+    const author = await guest('LbAuthor');
+    const liker = await guest('LbLiker');
+    const { id: uploadId } = await seedUpload(author.jwt, 'Lightbox heart');
+
+    await signIn(page, liker);
+    await page.goto('/feed');
+
+    // Open the lightbox by clicking the image button.
+    const imageButton = page.locator('article')
+      .filter({ hasText: author.displayName })
+      .first()
+      .getByRole('button', { name: 'Bild vergrößern' });
+    await expect(imageButton).toBeVisible({ timeout: 10_000 });
+    await imageButton.click();
+
+    // LightboxModal is `role="dialog"` (no aria-modal). The other dialog on the
+    // page is the ContextSheet which has `aria-modal="true"` even when closed,
+    // so scope to NOT-aria-modal to pick the lightbox specifically.
+    const lightbox = page.locator('[role="dialog"]:not([aria-modal])');
+    await expect(lightbox).toBeVisible();
+
+    // Find the inner image element to tap.
+    const media = lightbox.locator('img, video').first();
+    await expect(media).toBeVisible();
+
+    await doubleTap(page, media);
+
+    await expect.poll(async () => {
+      const feed = await api.getFeed(liker.jwt);
+      // Backend returns { uploads: [...], next_cursor }.
+      const list: any[] = feed.uploads ?? feed.items ?? feed;
+      const row = Array.isArray(list) ? list.find((u: any) => u.id === uploadId) : undefined;
+      return row?.like_count ?? row?.likes ?? 0;
+    }, { timeout: 5_000 }).toBeGreaterThanOrEqual(1);
+  });
+});