fix(review): worker-thread HEIC conversion with bomb guard, concurrency cap, and magic-byte routing (PR #151)

- Event-loop blockage: HEIC decode/encode (CPU-synchronous libheif WASM +
  jpeg-js) now runs in a per-conversion worker_threads Worker
  (src/web/heic-jpeg-worker.ts, spawned by heic-jpeg-converter.ts) with
  resourceLimits and a 30s hard timeout that terminates the worker —
  verified end-to-end under tsx and against compiled dist/ output with a
  real iPhone HEIC (event-loop max stall 52ms during conversion).
- No server-side concurrency cap: conversions now acquire a slot from the
  existing global runWithConversionLimit() pool (document-conversion-limiter),
  bounding peak decode memory/CPU across simultaneous uploads.
- Decompression bomb: header-declared dimensions are read via heic-decode's
  allocation-free `.all` path and rejected above 64MP BEFORE decode() can
  allocate width*height*4 bytes (a <300-byte crafted file can declare
  30000x30000 = 3.6GB). Regression-tested with a crafted ISOBMFF fixture
  against the real heic-decode WASM (test/heic-jpeg-core.test.ts).
- Mislabeled HEIC (documented Android/MIUI case): conversion now routes on
  ftyp magic-byte sniff of the raw buffer regardless of declared
  ext/Content-Type, so a HEIF uploaded as image/jpeg converts instead of
  415ing; the magic-mismatch 415 only fires for genuinely unrecognized bytes.
- Brand allowlist narrowed to what heic-decode's isHeic() accepts
  (heim/heis/hevm/hevs dropped — they could only ever fail conversion).
- Converted-output size: the JPEG result is checked against
  MAX_PASTE_IMAGE_BYTES (jpeg-js can inflate a within-limit HEIC past the cap).
- Deps: heic-convert replaced with its underlying heic-decode + jpeg-js
  (the wrapper could not expose the pre-decode dimension check); lockfile
  synced, drops pngjs.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

package.json

@@ -69,7 +69,8 @@
     "chokidar": "^3.6.0",
     "commander": "^12.1.0",
     "fastify": "^5.8.5",
-    "heic-convert": "^2.1.0",
+    "heic-decode": "^2.1.0",
+    "jpeg-js": "^0.4.4",
     "node-pty": "^1.1.0",
     "qrcode": "^1.5.4",
     "uuid": "^14.0.0",