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/helpers/upload-client.ts

@@ -0,0 +1,48 @@
+/**
+ * Node-side multipart upload helper. Lets adversarial specs post arbitrary
+ * bytes with arbitrary `Content-Type` claims to /api/v1/upload without
+ * driving the UI. Crucial for MIME-spoofing, oversize, polyglot, and
+ * filename-injection tests.
+ *
+ * Field shape matches [backend/src/handlers/upload.rs]:
+ *   - file       (binary; carries filename + content_type in the part headers)
+ *   - caption    (text, optional)
+ *   - hashtags   (CSV text, optional)
+ */
+// Node 22+ ships FormData and Blob as globals — no import needed.
+
+const BASE = process.env.E2E_FRONTEND_URL ?? 'http://localhost:3101';
+
+export type UploadOptions = {
+  filename?: string;
+  contentType?: string;
+  caption?: string;
+  hashtags?: string;
+};
+
+export async function uploadRaw(token: string, body: Uint8Array | Buffer, opts: UploadOptions = {}) {
+  const form = new FormData();
+  const blob = new Blob([body as any], { type: opts.contentType ?? 'application/octet-stream' });
+  form.append('file', blob as any, opts.filename ?? 'upload.bin');
+  if (opts.caption !== undefined) form.append('caption', opts.caption);
+  if (opts.hashtags !== undefined) form.append('hashtags', opts.hashtags);
+  return fetch(`${BASE}/api/v1/upload`, {
+    method: 'POST',
+    headers: { Authorization: `Bearer ${token}` },
+    body: form as any,
+  });
+}
+
+/** Convenience: read a fixture from disk and upload it. */
+export async function uploadFile(token: string, path: string, opts: UploadOptions = {}) {
+  const { readFile } = await import('node:fs/promises');
+  const body = await readFile(path);
+  return uploadRaw(token, body, opts);
+}
+
+/** Tiny valid JPEG header — magic bytes only, useful for "claim image but is N MB of zeros" tests. */
+export const JPEG_MAGIC = new Uint8Array([0xff, 0xd8, 0xff, 0xe0, 0x00, 0x10, 0x4a, 0x46, 0x49, 0x46]);
+/** Tiny valid PNG magic bytes. */
+export const PNG_MAGIC = new Uint8Array([0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a]);
+/** ELF header — the magic bytes of a Linux executable. `infer` reports `application/x-executable`. */
+export const ELF_MAGIC = new Uint8Array([0x7f, 0x45, 0x4c, 0x46]);