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.

assessments/CX_Discovery_Workshop/tests/conftest.py

@@ -0,0 +1,63 @@
+"""Test plumbing: import path + notebook content served from tagged cells.
+
+Content and client data live in the notebook, never in ``.py`` — the cells
+tagged ``topic-bank`` and ``engagement-data`` in
+``notebooks/cx_discovery.ipynb``. The fixtures below read those cells with
+nbformat and exec them, so pytest pins the exact content the deliverable
+ships (no kernel needed — tagged cells are self-contained by contract).
+
+The sys.path insert makes discoverylib importable even without the study
+venv active (the normal setup is ``pip install -e ".[dev]"`` into the
+study-local ``.venv/``).
+"""
+
+from __future__ import annotations
+
+import pathlib
+import sys
+from typing import Any
+
+import pytest
+
+STUDY_ROOT = pathlib.Path(__file__).resolve().parent.parent
+sys.path.insert(0, str(STUDY_ROOT))
+
+NOTEBOOK = STUDY_ROOT / "notebooks" / "cx_discovery.ipynb"
+
+
+def tagged_cell_ns(tag: str) -> dict[str, Any]:
+    """Exec the single cell carrying ``tag`` and return its namespace."""
+    import nbformat
+
+    nb = nbformat.read(NOTEBOOK, as_version=4)
+    cells = [c for c in nb.cells if tag in c.metadata.get("tags", [])]
+    assert len(cells) == 1, (
+        f"expected exactly one cell tagged {tag!r} in {NOTEBOOK.name}, "
+        f"found {len(cells)}"
+    )
+    ns: dict[str, Any] = {}
+    exec(compile(cells[0].source, f"{NOTEBOOK.name} [{tag}]", "exec"), ns)
+    return ns
+
+
+@pytest.fixture(scope="session")
+def topic_bank() -> dict[str, Any]:
+    """The executed namespace of the notebook's topic-bank cell."""
+    return tagged_cell_ns("topic-bank")
+
+
+@pytest.fixture(scope="session")
+def topics(topic_bank: dict[str, Any]) -> tuple[Any, ...]:
+    """The TOPICS tuple as the deliverable defines it."""
+    return topic_bank["TOPICS"]  # type: ignore[no-any-return]
+
+
+@pytest.fixture(scope="session")
+def topic_by_key(topics: tuple[Any, ...]) -> dict[str, Any]:
+    return {t.key: t for t in topics}
+
+
+@pytest.fixture(scope="session")
+def engagement() -> dict[str, Any]:
+    """The ENGAGEMENT dict as the deliverable's engagement-data cell ships it."""
+    return tagged_cell_ns("engagement-data")["ENGAGEMENT"]  # type: ignore[no-any-return]