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.

pyproject.toml

@@ -16,6 +16,7 @@ dependencies = [
     "pandas>=2.0",
     "plotly>=5.18",
     "numpy>=1.26",
+    "nbformat>=5.9",
 ]
 
 [project.optional-dependencies]
@@ -27,7 +28,7 @@ palladium = "core.cli.main:main"
 
 [tool.setuptools.packages.find]
 include = ["core*", "palladium*"]
-exclude = ["tests*", "studies*", "docs*"]
+exclude = ["tests*", "studies*", "assessments*", "docs*"]
 
 [tool.pytest.ini_options]
 testpaths = ["tests"]
@@ -44,4 +45,5 @@ ignore = ["E501"]  # line length handled by formatter
 
 [tool.ruff.lint.per-file-ignores]
 "studies/*/notebooks/*.ipynb" = ["E402"]
+"assessments/*/notebooks/*.ipynb" = ["E402"]
 "tests/*" = ["F401"]