fix: guard drag overlay to only trigger on external file drags

[tharunika-19]

Fixes #1515

What changed

Added e.dataTransfer?.types?.includes("Files") guard to the onDragEnter,
onDragLeave, and onDragOver handlers in FileUpload.tsx

Root Cause

The global dragenter listener had no filter — it triggered on ALL drag events
including slider drags, causing the "Drop your video anywhere" overlay to appear
when dragging the Brightness slider.

Fix

The guard checks if the drag contains actual files before showing the overlay.
Slider drags have empty dataTransfer.types, so they are now correctly ignored.

Tested

✅ Brightness slider adjusts value normally without triggering overlay
✅ Contrast and Saturation sliders unaffected
✅ Dragging a real video file from desktop still shows overlay correctly

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[github-actions]

👋 Thanks for your PR, @tharunika-19!

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[github-actions]

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[tharunika-19]

Hi @magic-peach! Could a maintainer please approve the workflows so the build check can run? The PR format check has passed and the fix is ready for review. Happy to make any changes if needed! 😊