Refresh tutorial: re-execute on v0.4.1, conform to current gallery

- Rebased onto main so the notebook inherits current conventions
  (py>=3.12, spatialdata-plot>=0.4.1 pin, repo rename, kernel name).
- Re-executed all cells against the released v0.4.1 (PercentileNormalize
  now ships in the release); refreshed committed outputs.
- Resolved the index.md conflict against the single-source gallery format
  (#11): card uses /notebooks/... absolute paths inside the gallery-cards
  markers, plus a toctree entry.
- Dropped the constant-value-channel edge case from section 12: in v0.4.1
  it neither warns nor renders mid-gray (every pixel collapses to the
  colormap floor), so the example contradicted its own prose. The two
  norm-validation examples (wrong-length list, invalid percentile bounds)
  remain and demonstrate the section's point correctly.

Author: timtreis