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/page-objects/lightbox.ts

@@ -0,0 +1,49 @@
+import type { Page, Locator } from '@playwright/test';
+
+export class Lightbox {
+  readonly page: Page;
+  readonly closeButton: Locator;
+  readonly nextButton: Locator;
+  readonly prevButton: Locator;
+  readonly likeButton: Locator;
+  readonly likeCount: Locator;
+  readonly commentInput: Locator;
+  readonly commentSubmit: Locator;
+  readonly commentsList: Locator;
+
+  constructor(page: Page) {
+    this.page = page;
+    this.closeButton = page.getByRole('button', { name: /schließen|close/i });
+    this.nextButton = page.getByRole('button', { name: /nächst|next/i });
+    this.prevButton = page.getByRole('button', { name: /vorherig|previous/i });
+    this.likeButton = page.getByRole('button', { name: /gefällt|like|heart/i }).first();
+    this.likeCount = page.locator('[data-testid="like-count"]').first();
+    this.commentInput = page.getByPlaceholder(/kommentar|comment/i);
+    this.commentSubmit = page.getByRole('button', { name: /senden|send|post/i }).first();
+    this.commentsList = page.locator('[data-testid="comments-list"]');
+  }
+
+  async close() {
+    await this.closeButton.click();
+  }
+
+  async like() {
+    await this.likeButton.click();
+  }
+
+  async addComment(text: string) {
+    await this.commentInput.fill(text);
+    await this.commentSubmit.click();
+  }
+
+  /** Swipe gesture support for mobile spec. */
+  async swipeLeft() {
+    const box = await this.page.locator('body').boundingBox();
+    if (!box) return;
+    const y = box.y + box.height / 2;
+    await this.page.mouse.move(box.x + box.width * 0.8, y);
+    await this.page.mouse.down();
+    await this.page.mouse.move(box.x + box.width * 0.2, y, { steps: 10 });
+    await this.page.mouse.up();
+  }
+}