Address the two items from the adversarial re-review of batch-2.
- upload: remove image/heic + image/heif from ALLOWED_MEDIA. Neither the
`image` crate nor the bundled ffmpeg 6.1 (Alpine 3.21 — HEIF demuxer
only landed in ffmpeg 7.0) can decode them, so accepting them stored
posts that never got a thumbnail. iOS Safari transcodes HEIC->JPEG on
file-input selection, so this rejects only the rare HEIC-preserving
path, now with a clear error instead of a silently broken post.
- data-mode-store: correct the stale "auth-gated" comment — the
/original route is intentionally unauthenticated (UUID-as-capability)
so it works from plain <img src> / <video src>.
Re-verified: cargo build (only the pre-existing middleware.rs warning).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>