Sibling fix to PR #28918 (Discord voice notes). DingTalk's rich-text
"voice" item type is its native voice-message format, but the adapter
was routing it to MessageType.AUDIO — which gateway/run.py:7605 skips
for STT. The docs claim every voice-capable platform auto-transcribes,
so this brings DingTalk in line.
Generic audio uploads (mapped to "file" by DINGTALK_TYPE_MAPPING) are
unchanged — they were already classified as DOCUMENT, not AUDIO.
Adds tests/gateway/test_dingtalk.py::TestExtractMedia covering both the
voice path and the audio-passthrough invariant.
93734c26e5