feat(flow): add support for new CrewAI Flow decorators (#40)

[cassiocouto]

Summary

Implements Issue #40 — adds detection for CrewAI Flow decorators and class inheritance.

• Config & regex patterns: Added @start, @listen, @router to CREWAI_FLOW_PATTERNS (config.py) and CrewAI usage_patterns (llm_patterns.py)
• Flow class inheritance detection: New _detect_flow_classes method in the AST scanner that detects class MyFlow(Flow) with alias-resilient matching (handles Flow as BaseFlow, crewai.flow.Flow, etc.)
• Flow relationship mapping: Enhanced _detect_decorators to extract @listen(...) / @router(...) arguments into metadata (listens_to, routes_from), supporting name refs, attribute refs (self.begin), string literals, and multiple arguments
• Semantic usage type: Flow-specific detections use UsageType.orchestration instead of generic UsageType.agent for better reporting
• Test fixture + 17 new tests: sample_crew_flow.py fixture and comprehensive TestCrewAIFlowDecorators class covering decorator detection, class inheritance (direct, aliased, attribute chain), relationship edge cases, and a full integration test

Files Changed

File	Change
src/ai_bom/config.py	Added @start, @listen, @router to CREWAI_FLOW_PATTERNS
src/ai_bom/detectors/llm_patterns.py	Added regex patterns for new decorators
src/ai_bom/scanners/ast_scanner.py	Added _detect_flow_classes, _collect_flow_aliases, _extract_decorator_refs; enhanced _detect_decorators
tests/fixtures/sample_crew_flow.py	New realistic CrewAI Flow fixture
tests/test_detection_enhanced.py	17 new tests + updated existing assertions

Test plan

• All 65 enhanced detection tests pass (tests/test_detection_enhanced.py)
• Full test suite: 759 passed, 21 skipped (only pre-existing SARIF Windows path test fails, unrelated)
• Ruff linting passes on all changed files

Closes #40