fix(config): Revert html_favicon default — gp-sphinx docs have no favicon

why: The shared default html_favicon="_static/favicon.ico" breaks CI
because gp-sphinx's own docs don't ship a favicon, and -W (warnings
as errors) makes the missing-file warning fatal. The workspace refactor
drop was intentional, not a regression. Downstream projects that need
favicons should pass html_favicon as an override.
what:
- Remove html_favicon from merge_sphinx_config() defaults
- Restore test asserting html_favicon is not in default output

Author: tony

packages/gp-sphinx/src/gp_sphinx/config.py

@@ -375,7 +375,6 @@ def merge_sphinx_config(
         # Static files and templates
         "html_static_path": list(DEFAULT_HTML_STATIC_PATH),
         "templates_path": list(DEFAULT_TEMPLATES_PATH),
-        "html_favicon": "_static/favicon.ico",
         # Theme (gp-sphinx child theme provides sidebars, templates, CSS, JS)
         "html_theme": DEFAULT_THEME,
         "html_theme_path": [],

tests/test_config.py

@@ -381,7 +381,7 @@ def test_merge_sphinx_config_html_paths() -> None:
     )
     assert result["html_static_path"] == ["_static"]
     assert result["templates_path"] == ["_templates"]
-    assert result["html_favicon"] == "_static/favicon.ico"
+    assert "html_favicon" not in result
     assert "html_extra_path" not in result