gigapdf-lib v0.71.1

Documentation-only patch. No code changes — the WASM blob is byte-for-byte
identical to 0.71.0.

Documentation

• Complete overhaul of the SDK documentation for 0.71: API reference (signature
  matrix for B / B-T / LTV signing, full ~263-method surface, removal of the
  phantom OCR methods doc.ocr / ocrText / extractText), USAGE guide (the
  four signing-signature levels + the host-fetch two-phase model + an SSRF note),
  COOKBOOK (added signTimestamped / signLtv recipes and an image-watermark
  recipe), plus the README and sdk/README (npm). No behavioural change — the
  WASM is identical to 0.71.0.