test(e2e): robustness — stable locators, exact assertions, no fixed sleep

- ContextSheet: add data-testid="context-sheet". longpress tests targeted the
  open sheet via the `.translate-y-0` animation class (breaks on any animation
  refactor) — now target `[data-testid="context-sheet"][aria-modal="true"]`,
  which is stable and unambiguous vs. the centered LightboxModal (also aria-modal).
- toast-on-failure: the like button was `button.filter(hasText:/\d+/).first()`,
  which could match any digit-bearing button (e.g. the comment count) → use the
  stable aria-label "Gefällt mir".
- config stats: assert the exact user_count (4 = 3 seeded guests + admin) instead
  of `>= 3` — deterministic after the per-test truncate, catches under/overcount.
- offline-network 429 test: replace the fixed 3s waitForTimeout with a
  poll-until-the-retry-count-stabilizes (faster, and a real storm never stabilizes
  → the poll fails, which is the intended outcome).

Note: reviewed the "config restore not in try/finally" finding — it's a non-issue.
The truncate auto-fixture wipes+reseeds the whole config table (and clears the
rate limiter) before every test, so config state cannot leak between tests.

All affected specs verified green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

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

@@ -45,13 +45,11 @@ test.describe('Mobile — long-press gesture', () => {
 
     await longPress(page, card, 600);
 
-    // The ContextSheet renders a dialog with role="dialog" + aria-modal="true".
-    // Multiple sheets (UploadSheet, ContextSheet) may be in the DOM — match the
-    // one that actually has aria-modal=true (i.e. the open one).
-    // ContextSheet is always mounted (it just translates off-screen when closed).
-    // Match the OPEN state by the `translate-y-0` class the component applies
-    // when `open === true`.
-    const sheet = page.locator('[role="dialog"][aria-modal="true"].translate-y-0');
+    // The ContextSheet is always mounted (it translates off-screen when closed).
+    // Target it by its stable data-testid, gated on aria-modal="true" which the
+    // component sets only while open — unambiguous vs. the centered LightboxModal
+    // (which also has aria-modal) and independent of the animation classes.
+    const sheet = page.locator('[data-testid="context-sheet"][aria-modal="true"]');
     await expect(sheet).toBeVisible({ timeout: 2_000 });
     await expect(sheet.getByRole('button', { name: /abbrechen/i })).toBeVisible();
   });
@@ -68,10 +66,9 @@ test.describe('Mobile — long-press gesture', () => {
     // Simulate a short press (200 ms — well under the 500 ms threshold).
     await longPress(page, card, 200);
 
-    // Within 1 s, no aria-modal=true dialog should be open (the ContextSheet
-    // is "open" only when its aria-modal flag is true).
-    // The ContextSheet stays mounted but `translate-y-0` is only set when open.
-    await expect(page.locator('[role="dialog"][aria-modal="true"].translate-y-0')).toHaveCount(0, { timeout: 1_000 });
+    // Within 1 s, the ContextSheet must not be open (aria-modal is set only when
+    // open). A quick tap opens the lightbox instead, which is a different element.
+    await expect(page.locator('[data-testid="context-sheet"][aria-modal="true"]')).toHaveCount(0, { timeout: 1_000 });
   });
 
   test('long-press suppresses the click that lands at pointerup (no double-open of lightbox)', async ({ page, guest, signIn }) => {