Add unit tests for doctrine infrastructure

[monkeypants]

Problem

The doctrine tests depend on infrastructure that has zero test coverage:

• core/parsers/ast.py (559 lines) — AST/griffe-based class extraction
• core/infrastructure/repositories/introspection/bounded_context.py (285 lines) — filesystem BC discovery
• core/use_cases/generic_crud.py (106 lines) — CRUD base classes for downstream projects

If any of these have a bug, doctrine tests produce false negatives (violations
pass silently). The parser in particular is the foundation — every doctrine test
routes through it.

Proposal

Add three test files, all pure additions with no changes to existing code:

core/parsers/tests/test_ast.py

• parse_python_classes() — finds classes in a directory of .py files
• parse_python_classes_from_file() — single-file extraction
• Class extraction: names, bases, fields, methods, docstrings
• _imported_class_names() — detects re-exported Request/Response classes
• parse_module_docstring() — extracts module-level docstrings
• Edge cases: empty files, syntax errors, non-existent paths, _-prefixed files
• parse_pipelines_from_file() — pipeline class detection with decorator/method checks

core/infrastructure/repositories/introspection/tests/test_bounded_context.py

• Discovers BCs with entities/ or use_cases/ directories
• Skips reserved words, dot-prefixed, non-packages
• Handles nested solutions (contrib/ containing BCs)
• Detects structural markers correctly
• Caching and cache invalidation
• get() by slug

core/use_cases/tests/test_generic_crud.py

• GetUseCase._get_by_id() — returns entity, raises EntityNotFoundError
• ListUseCase._list_all() — delegates to repo
• CreateUseCase._create() — generates ID, builds entity, saves
• UpdateUseCase._update_by_id() — fetches, applies model_copy, saves

All tests use tmp_path fixtures and in-memory fakes. No changes to
production code required.