PDFFence 1.19.0

Adds an opt-in Contents-bound signature coverage gate (PFP011). It requires aggregate evidence that a semantic signature’s two-pair current-file ByteRange gap exactly matches a direct hexadecimal /Contents token, without exposing offsets or signature material.

Validation: 245 tests, Ruff, reproducible wheel and source builds, Twine checks, clean Python 3.12/3.13 installs, and 156/156 PDFCAB fixtures.