f3b062a3a7
Adds docs/upload-file-types.md: the single Allowed File Types setting, every path it governs, the extension-to-MIME table, how to enable video, and what changed for chunked-upload/init (declared mimeType ignored, extension must be allowed, 400 File type not allowed). README links to it, and the Settings help text in EN and DE now says the list covers all upload paths and that video extensions must be added explicitly.