refactor(app): replace tab drag handling with dndkit (#33880)

Co-authored-by: opencode-agent[bot] <219766164+opencode-agent[bot]@users.noreply.github.com>

packages/app/src/components/titlebar-tab-gesture.ts

@@ -8,22 +8,6 @@ export function canStartTabDrag(pointerType: string) {
   return pointerType !== "touch"
 }
 
-export function isPrimaryPointerPressed(buttons: number) {
-  return (buttons & 1) !== 0
-}
-
-export function captureTabPointerDown(element: HTMLDivElement, clientX: number, clientY: number) {
-  const rect = element.getBoundingClientRect()
-  return {
-    startX: clientX,
-    startY: clientY,
-    grabOffsetX: clientX - rect.left,
-    grabOffsetY: clientY - rect.top,
-    width: rect.width,
-    element,
-  }
-}
-
 export function forwardTabRef(ref: Ref<HTMLDivElement> | undefined, element: HTMLDivElement) {
   if (typeof ref === "function") ref(element)
 }
@@ -31,7 +15,3 @@ export function forwardTabRef(ref: Ref<HTMLDivElement> | undefined, element: HTM
 export function canOpenTabRename(dragging: boolean | undefined, editing: boolean, committing: boolean) {
   return !dragging && !editing && !committing
 }
-
-export function createTabDragPreview(element: HTMLDivElement) {
-  return element.cloneNode(true) as HTMLDivElement
-}