DCAB 0.8.0

Added\n\n- binding.document_variable_value_changed: a deterministic pair that retains a fixed DOCVARIABLE field reference, stored field result, and variable name while changing only a persisted document-variable value.\n- Target-free truth for the new internal-state fact, with no field-evaluation or automation boundary.\n- DocFence adapter mapping for the document-variable inventory.\n\n## Contract\n\nThe fixture and observation schemas remain at version 1. The corpus has 19 paired cases. Every pair retains its package-member set and stored Word text-node sequence; the new pair changes only word/settings.xml.\n\n## Verification\n\nCI passed on Python 3.11, 3.12, and 3.13 plus the clean DocFence adapter.