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/10-flow-review/offline-resume.spec.ts

@@ -75,9 +75,7 @@ test.describe('Flow re-review — offline upload auto-resume (B1)', () => {
     // While offline: nothing may have reached the server, and — the crux of the
     // fix — the item must be parked as `pending`, NOT burned to `error`/`blocked`
     // (which on the old code would require a manual retry tap).
-    await expect
-      .poll(() => queueStatuses(page), { timeout: 8_000 })
-      .toEqual(['pending']);
+    await expect.poll(() => queueStatuses(page), { timeout: 8_000 }).toEqual(['pending']);
     expect(await db.countUploadsForUser(g.userId)).toBe(0);
 
     // Reconnect. The `online` listener must resume the queue automatically — we do
@@ -85,16 +83,17 @@ test.describe('Flow re-review — offline upload auto-resume (B1)', () => {
     await page.context().setOffline(false);
 
     // The queued upload is now created server-side without any manual interaction.
-    await expect
-      .poll(() => db.countUploadsForUser(g.userId), { timeout: 20_000 })
-      .toBe(1);
+    await expect.poll(() => db.countUploadsForUser(g.userId), { timeout: 20_000 }).toBe(1);
 
     // And the queue item ends terminal-good (done) or is drained — never stuck in error.
     await expect
-      .poll(async () => {
-        const s = await queueStatuses(page);
-        return s.every((x) => x === 'done') || s.length === 0;
-      }, { timeout: 10_000 })
+      .poll(
+        async () => {
+          const s = await queueStatuses(page);
+          return s.every((x) => x === 'done') || s.length === 0;
+        },
+        { timeout: 10_000 }
+      )
       .toBe(true);
   });
 });