images.ts bounded image parser

Snapshot image collection uses an in-module bounded PNG/JPEG header parser instead of image-size. Chose this over retaining the direct dependency because image-size@2.0.2 has two unresolved infinite-loop DoS advisories; header-only parsing avoids decoding untrusted JXL/HEIF/ICNS data while preserving the 40,000,000-pixel limit. Malformed or unsupported files are skipped with warnings.