chore: add changelog and documentation updates

- Created a new `CHANGELOG.md` file to document all notable changes to the project, adhering to the Keep a Changelog format.
- Updated `CONTRIBUTING.md` to include instructions for building and previewing documentation using MkDocs.
- Added `mkdocs.yml` configuration for documentation generation, including navigation structure and theme settings.
- Enhanced various documentation files, including API reference, architecture overview, configuration reference, and runbook, to provide comprehensive guidance for users and developers.
- Included new sections in the README for changelog and documentation links, improving accessibility to project information.

pyproject.toml

@@ -28,6 +28,11 @@ dev = [
     "pytest-asyncio>=0.24,<1.0",
     "httpx>=0.27,<1.0",
 ]
+docs = [
+    "mkdocs>=1.5,<2",
+    "mkdocstrings[python]>=0.24,<1",
+    "mkdocs-material>=9.0,<10",
+]
 
 [tool.setuptools.packages.find]
 where = ["."]