demo: restructure log header outside scrollable (always visible), remove sticky references, add Iced limitation note

examples/demo/styles.glts

@@ -379,6 +379,10 @@ Slider {
     width: fill
 }
 
+// Note: position:sticky is not supported by Iced. "Always visible header above
+// scrollable content" is the working pattern.
+// ═══════════════════════════════════════════════════════════════════════════════
+
 // ── Style Inheritance ────────────────────────────────────────────────────────
 .inherit {
     background: #f0ece6