test(trip): tighten description-clamp assertion + correct R11 coverage note

- trip-header.spec.js: replace the vacuous `toContainText('finally made
  sense')` (the tail text is in the DOM even while collapsed) with real
  clamp/un-clamp assertions — clientHeight < scrollHeight when collapsed,
  clientHeight >= scrollHeight once expanded — so the test actually proves the
  toggle changes visibility.
- trips-list.spec.js: the header comment claimed R11 coverage no fixture
  provided. Note that R11 (set-but-unresolvable cover_image) shares the exact
  else-branch the R7/AE3 fallback test exercises, so it's covered by
  construction in the shared cover macro.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RDS6t8wcpbwKvvrxykVQ5K

tests/ui/trip/trips-list.spec.js

@@ -1,5 +1,8 @@
 // @ts-check
-// Tests: U3 — trip-list card one-liner + retina cover (R5, R6, R7, R11, R14)
+// Tests: U3 — trip-list card one-liner + retina cover (R5, R6, R7, R14)
+// R11 (set-but-unresolvable cover_image falls back) shares the exact else-branch
+// exercised by the R7/AE3 fallback test below; it is covered by construction in
+// the shared cover macro rather than by a dedicated fixture here.
 const { test, expect } = require('@playwright/test');
 
 const DEMO_HREF = '/trips/italy-2026-demo';   // has a tagline, no cover_image (entry-image fallback)