docs: add comprehensive security and authentication documentation

Add new documentation sections covering security best practices and authentication system architecture. Update Sphinx configuration and dependencies to support documentation improvements.

Changes include:
- New security.rst with SSH key management, network security, secrets management
- New authentication.rst documenting pluggable auth system and provider setup
- Updated Sphinx config to use Alabaster theme and add sphinx-tabs extension
- Added docs extra dependencies in pyproject.toml for documentation builds
- Updated example configs to use Ed25519 instead of deprecated DSA keys
- Added .python-version file for consistent Python version management
- Added CLAUDE.md project instructions for AI-assisted development
- Minor Dockerfile cleanup removing commented pip install line

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

docs-sphinx-rst/source/conf.py

@@ -35,6 +35,7 @@ extensions = [
     "sphinx.ext.todo",
     "sphinx.ext.viewcode",
     "sphinx.ext.githubpages",
+    "sphinx_tabs.tabs",
 ]
 
 # Add any paths that contain templates here, relative to this directory.
@@ -124,22 +125,9 @@ todo_include_todos = True
 
 # -- Options for HTML output ----------------------------------------------
 
-try:
-    import sphinx_rtd_theme
-
-    html_theme = "sphinx_rtd_theme"
-    html_favicon = "_static/favicon.ico"
-    html_theme_path = [sphinx_rtd_theme.get_html_theme_path()]
-    html_context = {
-        "css_files": [
-            "_static/css/custom.css",  # overrides for wide tables in RTD theme
-            "_static/css/ribbon.css",
-            "_static/theme_overrides.css",  # override wide tables in RTD theme
-        ],
-    }
-except ImportError as e:  # noqa : F841
-    html_theme = "alabaster"
-    html_theme_path = []
+html_theme = "alabaster"
+html_theme_path = []
+html_favicon = "_static/favicon.ico"
 
 
 # The theme to use for HTML and HTML Help pages.  See the documentation for
@@ -381,7 +369,9 @@ texinfo_documents = [
 
 
 # Example configuration for intersphinx: refer to the Python standard library.
-intersphinx_mapping = {"https://docs.python.org/": None}
+intersphinx_mapping = {
+    "python": ("https://docs.python.org/3", None),
+}
 
 # -- Options for Epub output ----------------------------------------------