test: build comprehensive test suite reaching 80%+ coverage threshold

Add 22 test files (~700 tests) covering security-critical modules, core
infrastructure, API routes, and error handling. Final coverage: 86.73%
statements / 80.57% branches / 85.57% functions / 87.42% lines, all above
the 80% threshold enforced by jest.config.js.

Highlights:
- Unit tests for crypto-utils, credential-manager, auth-manager, csrf,
  input-validator, state-manager, health-checker, backup-manager,
  update-manager, resource-monitor, app-templates, platform-paths,
  port-lock-manager, errors, error-handler, pagination, url-resolver
- Route tests for health, services, and containers (supertest + mocked deps)
- Shared test-utils helper for mock factories and Express app builder
- npm scripts for CI: test:ci, test:unit, test:routes, test:security,
  test:changed, test:debug
- jest.config.js: expand coverage targets, add 80% threshold gate
- routes/services.js: import ValidationError and NotFoundError from errors
- .gitignore: exclude coverage/, *.bak, *.log

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

dashcaddy-api/package.json

@@ -8,6 +8,12 @@
     "test": "jest",
     "test:watch": "jest --watch",
     "test:coverage": "jest --coverage",
+    "test:ci": "jest --ci --coverage --maxWorkers=2 --forceExit",
+    "test:unit": "jest --testPathPattern=__tests__/(?!routes|integration) --no-coverage",
+    "test:routes": "jest --testPathPattern=__tests__/routes --no-coverage",
+    "test:security": "jest --testPathPattern=(crypto-utils|credential-manager|csrf-protection|auth-manager|input-validator|backup-manager) --no-coverage",
+    "test:changed": "jest --onlyChanged --no-coverage",
+    "test:debug": "node --inspect-brk node_modules/jest/bin/jest.js --runInBand --no-coverage",
     "lint": "eslint .",
     "lint:fix": "eslint . --fix",
     "format": "prettier --write '**/*.{js,json,md}'"