Media-type sniffing stays O(1) on ID3-prefixed input

Patch Changes

• 02ffdcb: fix(provider-utils): bound media-type sniffing decode for ID3-prefixed input

  Media-type detection stripped ID3 tags before the ~18-byte prefix cap, decoding the entire base64 attachment (plus a full-size copy) whenever the data began with ID3/SUQz. This turned the intended O(1) sniff into an O(N) decode of the whole attachment. Detection now decodes at most a bounded prefix and skips the ID3 tag within that bound, keeping cost O(1) in input size on all paths (image, audio, and combined).

• 76cb673: fix: detect MP4 audio from its ftyp box during transcription