initial: design + plan for kg-setup skill

Port the design spec and 17-task implementation plan from arb-scanner
(where the idea was born) to this dedicated repo. Paths in the plan
adjusted to treat this repo root as the skill root (no skills/kg-setup/
subdirectory). Implementation follows via subagent-driven-development.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitignore

@@ -0,0 +1,4 @@
+__pycache__/
+*.pyc
+.pytest_cache/
+.DS_Store