[G-Glitch404]

Summary

Add Sphinx-compatible objects.inv generation to the MkDocs documentation build.

This allows projects using Sphinx/Intersphinx to resolve and link to RESpx API objects such as respx.Router and respx.MockRouter.

Changes

• Replace mkautodoc with mkdocstrings[python]
• Enable Sphinx inventory generation
• Add a dedicated API objects documentation page
• Add an inventory validation Nox session
• Run the inventory validation as part of the documentation workflows
• Update documentation workflow path filters so relevant documentation changes trigger the build

Validation

The documentation build succeeds, and the generated site/objects.inv is checked for respx.Router and respx.MockRouter.

Closes #305