LR-IMP-FORMATS: HEIC/HEIF decode behind the optional heif feature

New crate `lightcraft-heif` (a port of PhotoCraft's photocraft-heif): a thin,
panic-guarded wrapper around heic-rs (pure Rust, pinned =0.1.1) - 8/10-bit,
alpha, grid tiles, container irot/imir/clap, ICC/EXIF/XMP. `lightcraft-codecs`
decodes HEIF behind its non-default `heif` feature (HEVC patents are the
distributor's call, the same policy as PhotoCraft); the apps forward it. HEIC
files stay recognised without the feature: opening one is a clear
"isn't included in this build" error. Fuzz-found heic-rs panics arrive as
regression fixtures (inline bytes, no media committed).

Verified end-to-end on real iPhone HEICs (lightcraft-cli render, rotation and
metadata correct). Note for reviewers: measured here, the engine currently
ignores the decoded image's source-space matrix on export for ANY format (a
true Display-P3 PNG round-trips unchanged); the ICC and space are carried for
all codecs, so this inherits - and does not worsen - existing behaviour.

Co-Authored-By: opencode <noreply@opencode.ai>

apps/lightcraft-cli/Cargo.toml

@@ -29,3 +29,7 @@ dhat = { workspace = true, optional = true }
 # every allocation (live/peak bytes in `library.memory` / `ui.inspect`) and writes dhat-heap.json
 # (open it in DHAT's viewer: allocation sites by bytes at the peak). Slows allocation-heavy work.
 dhat-heap = ["dep:dhat"]
+
+# Open HEIC/HEIF photos (the optional lightcraft-heif crate). Not default so distributors choose
+# it; official builds (CI, packaging/, release) build with `--features heif`.
+heif = ["lightcraft-codecs/heif"]