docs(api[components]): Registry-aware docutils component reference

[tony]

Summary

• Add docs/api/lib/components.md — a registry-aware reference covering every docutils component django-docutils ships: DjangoDocutilsWriter, DjangoDocutilsHTMLTranslator, the CodeTransform/Contents/SanitizeTransform transforms, the Pygments CodeBlock directive, and all twelve roles. Entries render with per-type kind badges and registry facts — transform default_priority as an outlined badge, the writer's resolved translator class, and the translator's own visit/depart overrides (including visit_icon, the translator-handled-node case that motivated the upstream feature).
• Enable the sphinx_autodoc_docutils and sphinx_autodoc_sphinx extensions and pin the component autodoc stack — sphinx-autodoc-docutils, sphinx-autodoc-sphinx, sphinx-ux-autodoc-layout, sphinx-ux-badges — at the released ==0.0.1a29 in the dev and docs dependency groups.
• Cross-link the component entries and the existing automodule pages both ways: each component-bearing module page gains a seealso pointing at its registry entry (api/lib/directives/code/ → components/#directive-codeblock, role pages → #role-<name>, …), and each components-page section links back to the full API page.

Companion

• gp-sphinx(feat[autodoc]): Component autodoc for docutils + Sphinx git-pull/gp-sphinx#53 — the component autodoc implementation this branch consumes (autowriter, autotranslator, autotransform(s), autodirective, autorole, and the docutils cross-reference domain). Merged and shipped in gp-sphinx 0.0.1a29, which this branch now pins directly from PyPI.

Design decisions

• One components page, not per-page embeds: embedding registry entries on each automodule page would register duplicate cross-reference targets; a single canonical page owns the anchors and the module pages link to them.
• sphinx_autodoc_sphinx enabled but inventory-empty: django-docutils registers nothing with Sphinx itself (no builders, domains, or config values) — the components page states this plainly so the docutils family reads as the complete inventory.
• Role names: entries derive names from the callables (github_role → github); prose notes that the names actually registered with docutils come from the DJANGO_DOCUTILS_LIB_RST roles mapping.

Test plan

• cd docs && just html builds clean with the released 0.0.1a29 autodoc stack installed; the components page renders the per-type kind badges, the transform priority badge, and the translator Overrides fact list (own handlers only)
• uv lock --check consistent; all four packages resolve to 0.0.1a29 from PyPI with no prerelease warnings
• CI: ruff / mypy / pytest on the branch

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.26%. Comparing base (fe006b5) to head (d078226).

Additional details and impacted files

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##           master     #461   +/-   ##
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  Coverage   84.26%   84.26%           
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  Files          48       48           
  Lines        1487     1487           
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  Hits         1253     1253           
  Misses        234      234           

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