feat(assistant): one-time disclaimer note + GA4 question-report guide

- Add a subtle disclaimer under the greeting (EN/MK/SI): "automated guide,
  can make mistakes — check the linked page for official steps." Shown once,
  not on every message, so it sets expectations without clutter. Persistent
  footer disclaimer stays.
- docs/GA4-ASSISTANT-REPORT.md: step-by-step for registering the custom
  dimensions and building the "top questions" + "unanswered questions"
  explorations in GA4 (dev-only doc, not deployed).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

assistant.css

@@ -52,6 +52,13 @@
 .msa-open .msa-panel { display: flex; animation: msa-rise .22s ease; }
 @keyframes msa-rise { from { opacity: 0; transform: translateY(12px); } to { opacity: 1; transform: none; } }
 
+/* one-time disclaimer note under the greeting */
+.msa-note {
+    font-size: 12px; line-height: 1.45; color: #6a787e;
+    background: #fff8ec; border: 1px solid #f0e3c8; border-radius: 10px;
+    padding: 8px 11px;
+}
+
 /* suggested-question chips */
 .msa-chips { display: flex; flex-wrap: wrap; gap: 8px; margin-top: 4px; }
 .msa-chips-label { width: 100%; font-size: 12.5px; color: #5a6b72; margin-bottom: 2px; }