Keep branch chart screenshots and sales.csv examples while integrating
main's --select docs and CI infrastructure. Workflow keeps bar,pie for
the 2D grouped sales example; bar/line auto-value sections combine
screenshots with solo --select override prose.

…rt screenshots

Grouping guide (grouping.mdx -> group.mdx) covered both --group mechanics
and how it compares to --select, with heavy repetition across sections.
Split into three focused pages: group.mdx (trimmed to just group
mechanics: pattern/regex syntax, bracket slots, aggregation, axis
labels), select.mdx (new, the --select flag reference across grouped
stat pick and solo value/mixed/multi-stat modes), and
group-vs-select.mdx (new, the decision guide plus auto-group/auto-value
inference rules previously scattered across other pages).

All /guides/grouping links across the docs (troubleshooting, commands,
charts, getting-started, index, features, examples/csv/README) updated
to /guides/group; group.mdx's own linked anchors (matching-separators,
bracket-slots, regex-syntax, the-dimensions, group-csvjson-data) were
preserved verbatim since troubleshooting.mdx and group-vs-select.mdx
link directly to them.

Also:
- Add pie/scatter chart screenshots (1D/2D/3D + value/mixed variants)
  referenced from charts/pie.mdx and charts/scatter.mdx.
- Fix a repo-wide typo: life-expentency-income.csv -> life-expectancy-income.csv
  (file, CSV example docs, and the CI workflow's example id/name).
- Add a clusters.csv CI example (2D auto-value scatter with visualMap)
  to the CSV examples workflow and README.
- Wording pass on CSV/JSON docs: "numeric columns become series" ->
  "numeric columns each become their own chart" (a --select-created
  chart isn't strictly a "series" anymore now that select.mdx exists).

Docs build (astro build) verified clean, 35 pages, no broken links.

Examples deploy workflows fired on every push to examples/**, which
could publish output from an unreleased vizb build. Trigger only on
Release completion or manual dispatch.

Swap embedded video for the existing contribution-history gif and
drop redundant install subsections (Go toolchain, nested headings).