Address P3 review feedback on notebook workflow

- Reword schedule comment: "smoke test" instead of overstating
  dataset URL breakage detection (loaders have fallbacks)
- Add "Keep in sync" comment on manual dep list, matching the
  convention in rust-test.yml python-fallback job
- Note why pip install -e . isn't used (requires Rust toolchain)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: igerber

.github/workflows/notebooks.yml

@@ -16,7 +16,7 @@ on:
       - 'pyproject.toml'
       - '.github/workflows/notebooks.yml'
   schedule:
-    # Weekly Sunday 6am UTC — catches external breakage (dataset URLs, etc.)
+    # Weekly Sunday 6am UTC — smoke test that notebooks still execute cleanly
     - cron: '0 6 * * 0'
 
 jobs:
@@ -33,9 +33,11 @@ jobs:
           python-version: '3.11'
 
       - name: Install dependencies
+        # Keep in sync with pyproject.toml [project.dependencies] and [project.optional-dependencies.dev]
         run: |
           pip install numpy pandas scipy matplotlib nbmake pytest ipykernel
           # Add repo root to Python path so Jupyter kernels can import diff_diff
+          # (pip install -e . requires the Rust/maturin toolchain; .pth avoids that)
           python -c "import site; print(site.getsitepackages()[0])" | xargs -I{} sh -c 'echo "$PWD" > {}/diff_diff_dev.pth'
 
       - name: Execute notebooks