Add story-to-pack research and a structured situation review

Research toward building a content pack from a story corpus, kept on its own
branch and independent of the game. Records the selection experiments against
blind labels, and settles selection as gate G2 followed by a human review:
review.py writes REVIEW.md and a review.json form, apply_review.py checks the
filled form and writes situations.json for the next stage.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01C6UDQ9o6L6Ey173U7XVou6

tools/story-to-pack/probe/validate-build.log

@@ -0,0 +1,8 @@
+V1: k=100 seed=15: 59 candidates, sampled 30
+V2: k=40 seed=14: 32 candidates, sampled 30
+V3: k=60 seed=16: 46 candidates, G2 accepts 13; growth stopped by gate 2, by cap 11
+blind sheet: 73 clusters, 1600 lines
+
+real	0m39.098s
+user	0m37.786s
+sys	0m1.160s