Add feature flags, seed data utilities, and Angular frontend scaffold

Major enhancements:
- Feature flag system for cloud vs air-gapped deployment modes
- Automatic storage backend selection based on deployment mode
- Comprehensive seed data generation utilities
- Support for generating CSV, JSON, binary, and PCAP test files
- Quick seed script for easy data generation
- Angular 19 frontend complete setup documentation
- Material Design UI component examples and configuration

Fixes:
- Resolve SQLAlchemy metadata column name conflict
- Rename metadata to custom_metadata throughout codebase
- Fix API health check issues

Documentation:
- FEATURES.md - Complete feature overview
- FRONTEND_SETUP.md - Angular 19 setup guide with examples
- SUMMARY.md - Implementation summary

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

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

app/models/artifact.py

@@ -22,7 +22,7 @@ class Artifact(Base):
     test_result = Column(String(50), index=True)  # pass, fail, skip, error
 
     # Additional metadata
-    metadata = Column(JSON)
+    custom_metadata = Column(JSON)
     description = Column(Text)
     tags = Column(JSON)  # Array of tags for categorization