fix: reorder forwardPanEvent conditions to skip expensive hasTextSelection on non-middle-button events (#9892)

## Summary

Reorder condition checks in `forwardPanEvent` so the cheap
`isMiddlePointerInput()` check runs first, avoiding expensive
`hasTextSelection()` → `window.getSelection().toString().trim()` on
every pointermove event.

## Changes

- **What**: `forwardPanEvent` now early-returns on
`!isMiddlePointerInput(e)` before calling `shouldIgnoreCopyPaste`, which
internally calls `hasTextSelection()`. Since most pointermove events are
not middle-button, this skips the expensive `toString()` call entirely.

## Review Focus

Semantic equivalence: the original condition was `(A && B) || C →
return`. Rewritten as two guards: `if (C) return; if (A && B) return;`.
The logic is equivalent — if `C` (`!isMiddlePointerInput`) is true, we
return regardless of `A && B`. If `C` is false (middle button), we check
`A && B` (`shouldIgnoreCopyPaste && activeElement`).

## Evidence

Backlog item #19. rizumu's Chrome DevTools profiling (Mar 2026) of a
245-node workflow showed `toString()` in `hasTextSelection` called on
every pointermove. Source: Slack `#C095BJSFV24` thread
`p1772823346206479`.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-9892-fix-reorder-forwardPanEvent-conditions-to-skip-expensive-hasTextSelection-on-non-middle--3226d73d365081d38b89c8bb1dde3693)
by [Unito](https://www.unito.io)

src/components/graph/GraphCanvas.vue

@@ -570,10 +570,8 @@ onUnmounted(() => {
   vueNodeLifecycle.cleanup()
 })
 function forwardPanEvent(e: PointerEvent) {
-  if (
-    (shouldIgnoreCopyPaste(e.target) && document.activeElement === e.target) ||
-    !isMiddlePointerInput(e)
-  )
+  if (!isMiddlePointerInput(e)) return
+  if (shouldIgnoreCopyPaste(e.target) && document.activeElement === e.target)
     return
 
   canvasInteractions.forwardEventToCanvas(e)