Security improvements:
- Add in-memory rate limiter for app password provisioning (5 attempts/hour/user)
- Returns 429 Too Many Requests with Retry-After header when limit exceeded
- Rate limiting is per-user to prevent cross-user DoS
Code quality improvements:
- Extract _extract_basic_auth() helper to reduce duplication across 3 endpoints
- Move base64, re imports to module level
- Add APP_PASSWORD_PATTERN constant for regex validation
- Add NEXTCLOUD_VALIDATION_TIMEOUT constant (10s)
Test coverage:
- Add test_provision_app_password_rate_limiting
- Add test_rate_limiting_is_per_user
- Add autouse fixture to clear rate limit state between tests
- Total: 15 tests for management API endpoints
Addresses reviewer feedback on PR #473.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
