feat(ui): add tat-anchored CSS class and rework setMode to dock the dialog in the page flow

src/ui.js

@@ -8,6 +8,12 @@ const STYLE = `
   font: 13px/1.4 Tahoma, Verdana, sans-serif;
   padding: 12px 14px;
 }
+.tat-root.tat-anchored {
+  position: static;
+  margin: 0 auto 12px;
+  max-width: 720px;
+  box-shadow: none;
+}
 .tat-header {
   display: flex; justify-content: space-between; align-items: center;
   padding-bottom: 8px; margin-bottom: 10px;
@@ -117,17 +123,37 @@ export class Dialog {
   setMode(mode, anchorInfo) {
     this.mode = mode;
     if (!this.root) return;
+    // Clear all position styles
     this.root.style.transform = '';
     this.root.style.top = '';
     this.root.style.bottom = '';
     this.root.style.left = '';
     this.root.style.right = '';
+    this.root.classList.remove('tat-anchored');
+
     if (mode === 'free') {
+      // Floating mode: ensure dialog is in body and position at bottom-left.
+      if (this.root.parentNode !== document.body) {
+        document.body.appendChild(this.root);
+      }
       this.root.style.bottom = '20px';
       this.root.style.left = '20px';
     } else if (anchorInfo && anchorInfo.canAnchor) {
-      this._positionAnchored(anchorInfo.rect);
+      if (anchorInfo.insertBefore) {
+        // Docked mode: insert the dialog into the page flow before the
+        // given element, and add the tat-anchored class to switch to
+        // static positioning.
+        anchorInfo.insertBefore.parentNode.insertBefore(this.root, anchorInfo.insertBefore);
+        this.root.classList.add('tat-anchored');
+      } else if (anchorInfo.rect) {
+        // Fallback: position fixed above the rect (old behavior, used when
+        // no insertion point is available but a rect was given).
+        this._positionAnchored(anchorInfo.rect);
+      }
+      // If neither insertBefore nor rect, leave the dialog where it is
+      // (the caller will show an anchorError note).
     } else {
+      // Top-center fallback (used when mode is anchored but no anchor info).
       this.root.style.top = '20px';
       this.root.style.left = '50%';
       this.root.style.transform = 'translateX(-50%)';