feat: add automated E2E quality test suite with ground truth validation

New E2EQualityTest (21 test methods) validates detection quality against
real spring-petclinic repo using Context7-sourced ground truth:

- Entity detection: all 6 JPA entities with table names
- Endpoint detection: all 16 REST endpoints with HTTP methods
- Controller/repository detection
- Framework detection (spring_boot present, no false quarkus/micronaut)
- Architecture stats (min nodes, edges, classes, methods, modules)
- Layer classification quality (entities/endpoints are backend)
- Edge quality (dependency edges exist)
- Determinism (two runs produce identical counts)
- ServiceDetector immutable map fix

Gated by E2E_PETCLINIC_DIR env var. Run with:
  E2E_PETCLINIC_DIR=/path/to/spring-petclinic mvn test -Dtest=E2EQualityTest

Tests: 1388 total (21 E2E + 1367 unit), 0 failures

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: aksOps