llama.cpp b10773 accepts data: URLs for video and audio input

The llama.cpp server in build b10773 now accepts data: URLs for the `input_video` and `input_audio` fields, resolving a previous issue where such inputs were incorrectly treated as raw base64 strings.

• The `handle_media()` function is updated to pass `true` for these content types, allowing video and audio MIME types in data URL validation.
• Malformed input now returns a 400 error instead of a 500 error by throwing `std::invalid_argument`.
• The `accept_base64_uri` flag has been removed from `handle_media`, simplifying the code.
• A unit test and updated comments are added to handle invalid data URI MIME types.

This change improves server robustness by providing clearer error handling for malformed media inputs.