docs(api): establish documentation infrastructure, autogenerated api reference, and agent standards

[MichalRedm]

Description

This PR resolves #8 by establishing a modern documentation infrastructure, an autogenerated API reference across all public subpackages of STRIDE, and codified documentation governance standards for AI agents.

Key enhancements:

• Documentation Website: Configured MkDocs with Material theme (mkdocs.yml), search, KaTeX math typesetting (pymdownx.arithmatex), dark/light mode toggle, and responsive navigation.
• Autogenerated API Reference: Created comprehensive reference pages under docs/api/ using mkdocstrings[python] with Google-style handler across stride.datasets, stride.drift, stride.models, stride.plotting, stride.xai.boundary, stride.xai.clustering, stride.xai.importance, stride.xai.recurrence, stride.xai.stats, and stride.exceptions.
• Narrative Guides & Scientific Documentation: Added structured user guides, getting started documentation, drift taxonomy, and mathematical formulations for concept drift and xAI metrics.
• Docstring Refactoring: Standardized core algorithms and classes across src/stride/ to strict Google-style docstrings (parameter types strictly in Python 3.10+ signatures, LaTeX math syntax, explicit Raises sections).
• Tooling & Packaging: Added docs extra and included it in all in pyproject.toml; configured Ruff pydocstyle Google convention with D417 enforcement.
• CI/CD Automation: Added .github/workflows/docs.yml to run strict documentation builds (mkdocs build --strict) on pull requests and deploy automatically to GitHub Pages on release or push to main.
• Agent Governance: Authored .agents/rules/documentation_standards.md and integrated triggers in AGENTS.md, .agents/acs.yaml, and .agents/rules/python_package_standards.md.

Closes #8

Type of Change

• Documentation update
• New feature (non-breaking change which adds functionality)
• Code style update / refactoring
• CI/CD pipeline configuration

Verification

• ruff check . passes with zero errors (All checks passed!)
• ruff format --check . passes with zero formatting issues (113 files already formatted)
• python -m unittest discover tests passes with 42 tests passing (OK)
• mkdocs build --strict builds successfully in strict mode with 0 warnings