server : accept data: URLs for input_video and input_audio (#27735)

* server : accept data: URLs for input_video and input_audio

input_video and input_audio passed accept_base64_uri=false to
handle_media(), so data: URLs got treated as raw base64 strings and
failed later with a confusing media probe error (#27724).

pass true for these two content types the same way image_url already
does, and allow video/audio mime types in the data: url check instead
of image only. data URL validation now throws std::invalid_argument so
malformed input comes back as 400 instead of 500, matching the other
input validation in this file.

* server : simplify handle_media and drop unused accept_base64_uri flag

* server : update comment and add unit test for invalid data URI MIME

tools/server/tests/unit/test_vision_api.py

@@ -71,6 +71,7 @@ def test_v1_models_supports_multimodal_capability():
         ("What is this:\n", "malformed",              False, None),
         ("What is this:\n", "https://google.com/404", False, None), # non-existent image
         ("What is this:\n", "https://ggml.ai",        False, None), # non-image data
+        ("What is this:\n", "data:text/html;base64,aGVsbG8=", False, None), # unsupported data uri mime
         # TODO @ngxson : test with multiple images, no images and with audio
     ]
 )