Add validate-provenance.sh and validate-provenance.bats to enforce the
sources provenance chain introduced by skill-author. Eight checks cover
slug cross-references, Contributing files existence, bidirectional
source_keys linkage, Research doc: field presence, and upstream research
doc alignment (forward INFO, reverse FAIL). Adds a new Provenance report
dimension and INFO finding level (observational, exit-0, counted
separately as · P info in the result block).
Closes#8
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>