Add comprehensive unit tests for search_app_vulnerabilities (mcp-k7c)

Phase 4 of vulnerability consolidation adds 4 critical unit tests:

- useLatestSession fallback: Verifies warning when no session found
- Null SDK response: Tests error handling for null API responses
- Session metadata filtering: Case-insensitive metadata matching with pagination
- Standard filters: Validates all filter parameters pass correctly to SDK

All 270 tests passing (up from 266).

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

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

Author: ChrisEdwards