docs: audit and fix documentation accuracy

[rootLocalGhost]

• Removed duplicated bullet points under "High-Performance Engine" and "Cinema Player Experience" in README.md
• Updated toggle_favorite signature in API.md
• Updated upload_playlist_cover and upload_playlist_banner signatures in API.md
• Updated delete_video signature in API.md
• Updated upload_artist_avatar signature in API.md
• Updated get_video_metadata signature in API.md
• Updated reindex_library signature in API.md
• Updated download_video signature in API.md
• Updated get_videos_by_artist signature in API.md
• Updated update_playlist_title signature in API.md

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PR created automatically by Jules for task 2882448203120018758 started by @rootLocalGhost

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