feat: add HEIC/HEIF format support for input and output

Add bidirectional HEIC support using system libheif CLI tools (heif-enc/heif-dec)
for HEVC encoding/decoding, since Sharp's bundled libheif only supports AV1.

- HEIC input: all tools now accept iPhone HEIC photos via heif-dec pre-processing
- HEIC output: convert tool produces true HEIC (HEVC) via heif-enc
- Docker: adds libheif-examples package for heif-enc/heif-dec CLI tools
- Tests: full conversion matrix (7x7), unit tests, and Playwright e2e tests
- Docs: updated OpenAPI spec, image-engine docs, getting-started, llms-full.txt

packages/image-engine/src/engine.ts

@@ -56,7 +56,7 @@ const OPERATION_MAP: Record<
   invert: (img) => invert(img),
 };
 
-const FORMAT_MAP: Record<OutputFormat, string> = {
+const FORMAT_MAP: Record<string, string> = {
   jpg: "jpeg",
   png: "png",
   webp: "webp",