By: Michael Lynch <git@mtlynch.io>
Tighten FileID type and rename OriginalExt to StoredExt - FileID is now a struct validated against lowercase UUID format on construction; NewFileID returns (FileID, error) - Rename OriginalExt to StoredExt and return error on unknown media type to reflect that the extension is post-conversion, not the upload original - Replace magic numbers 850/250/150 with named display-width constants - Wire thumbnail width constants into the browse template sizes attribute Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>