feat: add master notebook library scaffolding and review tooling

Add CLAUDE.md defining the Palladium master notebook conventions and
Red Panda Approval criteria, plus a review-notebook slash command for
LLM-driven notebook review.

Expand .gitignore to block client/engagement documents and generated
exports, keeping masters client-clean while allowing text/image sources.

Normalize slider widget numeric values from floats to integers in
notebook JSON.

.gitignore

@@ -7,8 +7,26 @@
 
 # Palladium-specific
 .env
+.DS_Store
+
+# Generated exports — never committed (masters and assessments)
 studies/*/exports/*
 !studies/*/exports/.gitkeep
+assessments/*/exports/*
+!assessments/*/exports/.gitkeep
+
+# Client / engagement documents must NEVER be committed — masters stay
+# client-clean (see CLAUDE.md, Confidentiality). Text/image source material
+# is allowed; binary documents are blocked by default. ONE exception: a
+# Study's published, public source PDF — add with `git add -f` and say so
+# in the commit message.
+studies/*/docs/*
+!studies/*/docs/*.md
+!studies/*/docs/*.png
+assessments/*/docs/*
+!assessments/*/docs/*.md
+!assessments/*/docs/*.png
+*SOW*
 
 # IPython
 profile_default/