fix: bubble menu always positioned at selection end

Changed from selectionStart to selectionEnd so bubble follows where user finished selecting. Removed broken fallback that repositioned to textarea bottom on every scroll. Simple viewport clamp instead.

frontend/editor-poc.html

@@ -782,15 +782,14 @@ body { font-family: var(--sans); background: var(--bg); color: var(--text); heig
   // ---- Bubble menu ----
   function showBubble() {
     if (ta.selectionStart === ta.selectionEnd) { hideBubble(); return; }
-    // Position below the selection start, using caret pixel calc
-    var pt = caretToPixel(ta.selectionStart);
-    // Convert from editorWrap-relative to viewport-relative
+    // Position below selection END (where user finished selecting)
+    var pt = caretToPixel(ta.selectionEnd);
     var wr = editorWrap.getBoundingClientRect();
     var top = wr.top + pt.y + 4;
     var left = wr.left + pt.x - 10;
-    // Fallback if caret calc gives odd values
-    if (top < 50) { var tr = ta.getBoundingClientRect(); top = tr.bottom + 6; left = tr.left + (tr.width / 2) - (bubble.offsetWidth / 2); }
-    if (top + 36 > window.innerHeight) top = top - 60;
+    // Clamp to viewport (never use textarea fallback)
+    if (top < 60) top = 60;
+    if (top + 40 > window.innerHeight - 10) top = window.innerHeight - 50;
     if (left < 6) left = 6;
     if (left + bubble.offsetWidth > window.innerWidth - 6) left = window.innerWidth - bubble.offsetWidth - 6;
     bubble.style.left = left + 'px'; bubble.style.top = top + 'px';