test: Add unit tests for config_loader, hybrid_analyzer, semgrep_scanner

New test coverage for three core modules:
- config_loader: defaults, env var overrides, profile loading, boolean parsing
- hybrid_analyzer: initialization, finding creation, heuristic integration
- semgrep_scanner: PATH resolution (str vs list), build_cmd, python -m fallback

116 tests passing, coverage 3% → 6%.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: devatsecure