feat: Rewrite Python extractor on tree-sitter AST with Django support

[GertL]

Summary

• Replace the regex/line-scanner Python extractor with a tree-sitter AST parser. All prior facts are preserved; the AST additionally emits RelCalls / RelInstantiates edges from function bodies, return type annotations, and structural decorator props (@staticmethod, @classmethod, @Property, @AbstractMethod, @task, @shared_task).
• Add Django project detection (via dependency files / manage.py); classify models with auto-derived table names, CBVs, DRF serializers, @api_view routes, and urls.py path patterns.
• Fix stale pointer bug: ownerStack and route back-fill now use slice indices instead of *facts.Fact pointers, preventing silently lost call edges when w.out reallocates during body traversal.
• Skip @overload-decorated functions to avoid duplicate symbol facts for type-checker-only stubs (verified on Apache Airflow: 131 → 79 duplicates eliminated).