Revert label-manager/dropdown-controller overabstractions, fix flaky viewport test

- Inline label-manager.ts and dropdown-controller.ts back into core/index.tsx —
  they created DI interfaces for code with exactly one consumer
- Keep the actual improvements: cancelAllLabelFades() for orphaned timer cleanup,
  clearAllLabels() for combined clear+cancel
- Fix flaky "should handle elements outside viewport" test: use scrollIntoViewIfNeeded()
  instead of fixed scrollPage(1000) which was viewport-size-dependent

584/584 e2e tests pass, 0 flaky.

Made-with: Cursor

Author: aidenybai

packages/react-grab/e2e/edge-cases.spec.ts

@@ -324,8 +324,10 @@ test.describe("Edge Cases", () => {
   test.describe("Viewport Edge Cases", () => {
     test("should handle elements outside viewport", async ({ reactGrab }) => {
       await reactGrab.activate();
-      await reactGrab.scrollPage(1000);
-      await reactGrab.page.waitForTimeout(500);
+
+      const footer = reactGrab.page.locator("[data-testid='footer']");
+      await footer.scrollIntoViewIfNeeded();
+      await reactGrab.page.waitForTimeout(200);
 
       await reactGrab.hoverElement("[data-testid='footer']");
       await reactGrab.waitForSelectionBox();