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/01-auth/pin-reset-lifecycle.spec.ts

@@ -9,8 +9,7 @@
  *   - a host reset REVOKES the target's sessions (the forgotten/compromised device is logged out)
  */
 import { test, expect } from '../../fixtures/test';
-
-const BASE = process.env.E2E_FRONTEND_URL ?? 'http://localhost:3101';
+import { BASE } from '../../helpers/env';
 
 const requestReset = (displayName: string) =>
   fetch(`${BASE}/api/v1/recover/request`, {
@@ -59,9 +58,8 @@ test.describe('PIN reset — in-app request lifecycle', () => {
     api,
     host,
     db,
-    adminToken,
   }) => {
-    // The admin user exists (adminToken logged them in). Their display name is "Admin" by
+    // The admin user exists (the host fixture logs an admin in to create it). Its display name is "Admin" by
     // convention; request a reset for it and confirm the queue stays empty — the INSERT filters
     // `role <> 'admin'`, so queuing a reset for an admin would be a privilege-relevant leak.
     const admin = (await api.listUsers(host.jwt)).find((u: any) => u.role === 'admin');