Consolidate the tutorials to eight notebooks

## Rulings

> User decisions 2026-09-11. Target set, eight marimo notebooks in two groups. Data
> operations (3): BrainData (loading, indexing, arithmetic, saving, plotting, NeuroVault, and
> a masks-and-ROIs section that includes brain space and resolution), DesignMatrix,
> Adjacency. Analysis (5): univariate GLM (the real eight-subject workflow; the simulated
> per-subject port becomes its opening), prediction (decoding, classification and ROC,
> encoding, spatial scales), similarity and RSA, functional alignment with decomposition as a
> closing section, intersubject correlation. No Roc or Simulator tutorials: users meet them
> through the class methods and the reference. Sources: the twelve v0.5.1 ports under
> data-operations/ and analysis/, and the seven 0.6.0 notebooks under basics/ and workflows/;
> the duplication audit lists the overlaps and what each source uniquely covers. Each target
> notebook is built from its sources, keeps every unique section the audit lists, states each
> caveat once, stays trimmed (aim under 400 lines), runs clean under the stderr gate, and
> caches fits in .tutorial-cache. Delete the source notebooks, update docs/tutorials/index.md
> (one line per notebook, the community links live here only), zensical.toml nav, the
> tutorials-check/tutorials-run tasks and CLAUDE.md. Gate: uv run poe tutorials, uv run poe
> docs-build, uv run poe ok, then prose review and unslop.

> User decisions 2026-09-08 (the consolidation decision this target came from): port-first
> (all twelve v0.5.1 examples one-to-one as marimo notebooks in the two original groups, then
> prune and merge in a second pass); document decompose/component_viewer, upload_neurovault,
> Simulator, and restore the v0.5.1 README community links.

> Amended 2026-09-12: the lineage labelling of the nav groups is done by the docs re-cut,
> which re-cuts the nav first; this slice starts from the labelled nav and goes straight to
> building the eight notebooks.

Also fold in the tutorial items from #489: an "open in molab" button per tutorial, and
suppressible UserWarnings so the rendered pages are clean.

Blocked by: #506
Blocks: #507

Start from the labelled nav and the twelve v0.5.1 sources under data-operations/ and analysis/ plus the seven 0.6.0 notebooks under basics/ and workflows/. Review the duplication audit, then build the eight target notebooks, update docs/tutorials/index.md, zensical.toml, the tutorials-check/tutorials-run tasks, and CLAUDE.md. Done means the sources are deleted, the tutorials cache fits, and uv run poe tutorials, uv run poe docs-build, and uv run poe ok pass, followed by prose review and unslop.

Written by the indexing model from the issue text.