Media-type detection was duplicated across Media, MediaItem (byte-identical copies), HasMedia::getMediaType, the ContentTypeCompatibleWithMedia rule, and six publishers — each hardcoding MIME prefixes and divergent extension lists (Media's video list even had avi/webm/mkv, contradicting the Type enum's mp4/mov).
Add classify(), fromExtension(), and isGif() to Media\Type as the single source for 'what kind is this?' (broad classification), distinct from fromMime()/allowedMimeTypes() (the strict upload allow-list). Every detector now delegates to the enum; the broad extension lists and MIME prefixes live only there. Behavior-preserving (full suite green); adds direct tests for classify/fromExtension/isGif.
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