feat(api-style): Add badge system for standard Python API entries

[tony]

Summary

• Adds gp_sphinx.api_style Sphinx extension that injects type and modifier badges into standard Python domain entries (functions, classes, methods, properties, attributes, data, exceptions)
• Ships complete CSS with gas- prefix, 8 distinct type colors (function=blue, class=indigo, method=cyan, property=teal, attribute=slate, data=grey, exception=rose, type=violet), light/dark mode, Furo integration
• Mirrors the badge visual language from sphinx-autodoc-pytest-fixtures (spf- prefix) so API pages and fixture pages look consistent

Architecture

Pure doctree transform — hooks into doctree-resolved, walks addnodes.desc nodes, detects modifiers from desc_sig_keyword nodes and deprecation from versionmodified, injects badge groups. No directive or documenter overrides, so cross-references and object IDs are preserved.

Badge types

Badge	Style	Detected from
function, class, method, property, attribute, data, exception	Filled, type-specific color	desc.objtype
async	Purple outlined	desc_sig_keyword("async")
classmethod	Amber outlined	desc_sig_keyword("classmethod")
staticmethod	Grey outlined	desc_sig_keyword("static")
abstract	Indigo outlined	desc_sig_keyword("abstractmethod")
final	Emerald outlined	desc_sig_keyword("final")
deprecated	Red/grey outlined	versionmodified(type='deprecated')

Files

Extension (packages/gp-sphinx/src/gp_sphinx/api_style/):

• __init__.py — setup(), CSS registration, abbreviation visitor
• _css.py — CSS class constants (gas-* prefix)
• _badges.py — Badge group builder with canonical ordering
• _transforms.py — Doctree-resolved handler, modifier/deprecated detection
• _static/css/api_style.css — Full CSS token system, light/dark, Furo integration

Tests (tests/ext/api_style/): 37 unit tests + 11 doctests

Docs (docs/packages/api-styling.md): Live demo page with synthetic API module

Bugfixes included

• Fix nested desc traversal so methods get their own objtype (not parent class)
• Fix deprecated detection to exclude nested desc nodes (class doesn't inherit method's deprecation)
• Fix worktree-safe doctest in docs/_ext/package_reference.py

Test plan

• uv run ruff check . --fix --show-fixes — all checks passed
• uv run ruff format . — no changes
• uv run mypy src tests — no issues in 33 source files
• uv run pytest --reruns 0 — 711 passed, 3 skipped
• uv run sphinx-build -b html docs docs/_build/html — build succeeded
• Visual review of badge rendering on demo page

[codecov-commenter]

Codecov Report

❌ Patch coverage is 94.63519% with 25 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.17%. Comparing base (c36fbd6) to head (dee1c36).

Files with missing lines	Patch %	Lines
...-style/src/sphinx_autodoc_api_style/_transforms.py	84.41%	12 Missing ⚠️
docs/_ext/gas_demo_api.py	75.86%	7 Missing ⚠️
scripts/ci/package_tools.py	20.00%	4 Missing ⚠️
...api-style/src/sphinx_autodoc_api_style/__init__.py	92.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #10      +/-   ##
==========================================
+ Coverage   88.82%   89.17%   +0.35%     
==========================================
  Files          72       78       +6     
  Lines        7111     7576     +465     
==========================================
+ Hits         6316     6756     +440     
- Misses        795      820      +25     

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