fix: browser test fixes and typecheck script

- Fix widgetTextBox locator in ComfyPage
- Add exact match for 'Add' button in search filter panel
- Fix ClipboardHelper to properly handle undefined vs null locators
- Use canvasOps.dragAndDrop in NodeOperationsHelper
- Use nodeOps.waitForGraphNodes in link interaction tests
- Add typecheck:browser script for browser tests

Amp-Thread-ID: https://ampcode.com/threads/T-019c1696-c595-7724-8dca-64f73f19f478
Co-authored-by: Amp <amp@ampcode.com>

browser_tests/fixtures/helpers/NodeOperationsHelper.ts

@@ -119,13 +119,13 @@ export class NodeOperationsHelper {
       y: nodePos.y + nodeSize.height * ratioY
     }
     // -1 to be inside the node.  -2 because nodes currently get an arbitrary +1 to width.
-    await this.comfyPage.dragAndDrop(
+    await this.comfyPage.canvasOps.dragAndDrop(
       { x: bottomRight.x - 2, y: bottomRight.y - 1 },
       target
     )
     await this.comfyPage.nextFrame()
     if (revertAfter) {
-      await this.comfyPage.dragAndDrop(
+      await this.comfyPage.canvasOps.dragAndDrop(
         { x: target.x - 2, y: target.y - 1 },
         bottomRight
       )