Add API Documentation Support

This release adds comprehensive API documentation support using Griffe for Python code analysis.

New Features

API Documentation Plugin System: Extensible plugin architecture for generating API docs from source code
Python Plugin: Extract API documentation from Python packages using Griffe with support for Google, NumPy, and Sphinx docstring styles
CLI Command: cross-docs generate-api to generate API documentation JSON
React Components: Full set of components for rendering API docs:
- APIPage / APILayout - Main page and layout with separate sidebar
- ModuleDoc / ClassDoc / FunctionDoc - Documentation renderers
- Signature / Docstring / ParameterTable - Specialized display components
Sidebar Improvements: Collapsible sections and compact mode for large navigation structures
Custom Header Support: APILayout accepts custom header/footer components for branding

Add to your pyproject.toml:

[[tool.cross-docs.api]]
plugin = "python"
package = "my_package"
prefix = "/api"
docstring_parser = "google"

Fixed API navigation URLs to use dotted paths (e.g., /api/pkg.module instead of /api/pkg/module/) for cleaner URLs
Fixed prefix calculation for multi-docs API references (e.g., /docs/django/api-reference/)