chore: install missing supertest devDependency for API route tests

Issue:
- tests/unit/api-routes.test.js failed with ERR_MODULE_NOT_FOUND for 'supertest'
- supertest was listed in package.json devDependencies but not installed
- Root cause: NODE_ENV=production prevents devDependencies installation by default

Solution:
- Ran NODE_ENV=development npm install to install devDependencies
- Verified supertest installation in node_modules/supertest/
- API route tests now running successfully

Dependencies Added:
- supertest@^7.1.4 (already in package.json, now installed)
- superagent (supertest dependency)
- 28 other transitive devDependencies

Test Results:
- tests/unit/api-routes.test.js now loads successfully
- POST /api/scans/start tests passing
- POST /api/scans/start-multi tests passing

Note:
- The issue occurred because NODE_ENV is set to "production" globally
- Future devDependency installations require NODE_ENV=development override
- Alternative: Use npm install --include=dev

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

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

Author: aledlie