Implemented the analyzer plugin framework with AnalyzerProtocol,
AnalyzerRegistry for registration/discovery by file extension,
PythonAnalyzer (AST-based extraction of modules, classes, functions,
imports, docstrings), and MarkdownAnalyzer (section, code block, and
link extraction). Both analyzers produce well-formed UKO triples with
proper URI schemes.
ISSUES CLOSED: #551
