Add copy feedback for file name copy in Upload Panel

[aditigupta217]

closes #572
Adds visual copy feedback to the "Copy" action in the Upload Panel, which copies the uploaded file's name to the clipboard. Previously, clicking Copy gave no indication of whether the action succeeded or failed, creating uncertainty for users.

• Added success/failure feedback states to the file name copy button:
  • On success: button label changes to "Copied!" for ~1.5–2 seconds, then reverts to "Copy".
  • On failure (e.g., clipboard permission denied, unsupported browser): button shows "Couldn't copy" instead of failing silently.

[vercel]

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[imDarshanGK]

@aditigupta217