feat: render HLS/HEIC inline + compress uploads + transcode GIFs

[barrydeen]

Summary

• Renders .m3u8 (HLS) and .heic/.heif URLs as inline video/image inside notes — the HLS module and Coil3 ImageDecoder support were already on the classpath; only the extension/MIME sets in the content parser needed updating.
• Adds a shared preprocessing pipeline on every Blossom upload path (profile picture, compose attachment, DM attachment):
  • Images are decoded via ImageDecoder (handles HEIC natively on API 28+), EXIF-rotated when needed, proportionally scaled, and JPEG re-encoded. Profile pictures cap at 400px / quality 75; compose and DM content cap at 1920px / quality 82.
  • GIFs are transcoded to muted H.264 MP4 via MediaCodec + MediaMuxer through an EGL input surface (typical 5–20× size reduction). No new Gradle deps.
  • Videos and other file types pass through unchanged.
• imeta dim and Kind-15 size/dim tags are recomputed from post-pipeline bytes so clients see metadata that matches what was actually uploaded. Gallery-mode mixing check now treats GIFs as video since they become MP4s.

Test plan

• Paste a note containing https://test-streams.mux.dev/x36xhzz/x36xhzz.m3u8 in the feed — renders as an inline video player and plays.
• Paste a note with a .heic URL — renders as an inline image on API 28+.
• Pick a 4000×3000 HEIC from the gallery as profile picture — upload succeeds, picture URL renders, bytes are ≤ ~40 KB, width ≤ 400, MIME image/jpeg.
• Attach a large JPEG (≥ 4 MB) in compose — compressed bytes ≤ ~500 KB at 1920-wide; published note's imeta dim reflects compressed dimensions.
• Attach a .heic in compose — uploads successfully as .jpg, renders in Damus/Amethyst.
• Send an image in a DM — encrypted upload uses compressed bytes; Kind 15 dim/size reflect post-compression values.
• Attach a GIF via the Android GIF keyboard in compose — uploaded URL ends in .mp4, dramatically smaller than the GIF, renders as an inline video that auto-plays muted.
• Repeat GIF flow in DM.
• Edge cases: 1-frame GIF, long GIF (>10s), tiny GIF (<100 px) — no crashes.
• ./gradlew assembleDebug passes.