Fix(video): show loading state during uploads

[Found-L]

Summary

• add a loading state while videos are being uploaded
• prevent duplicate submissions during upload
• support file type and size validation
• support single and multiple video uploads
• handle upload failures and allow retrying the same file
• document the video upload options and behavior

New options

• acceptMimes
• maxSize
• multiple
• onError

Validation

• pnpm lint
• pnpm type-check
• pnpm build:lib
• VitePress documentation build
• git diff --check

Closes #369

[vercel]

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