refactor+feat: Snapshot-Router-Split + generischer ChecklistAgent + AGB-Modul

- Item 2: Snapshot-Doc-Checks (cookie/impressum/dse/agb) in snapshot_check_routes.py
  (agent_compliance_check_routes.py 464→365 Z.); gleiche Pfade, in main.py registriert.
- ChecklistAgent-Basis: DSE-Logik generalisiert (L1/L2, kurze Titel, _severity_
  override-Hook). DSEAgent + AGBAgent sind jetzt Thin-Subclasses → künftige
  Doc-Agenten (widerruf/avv/…) trivial.
- Item 4: AGBAgent (§§ 305 ff. BGB, AGB_CHECKLIST) + agb-check + AGB-Tab via
  AgentModuleTab. Kein Library-Firehose.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend-compliance/main.py

@@ -50,6 +50,7 @@ from compliance.api.agent_recurring_routes import router as agent_recurring_rout
 from compliance.api.agent_compare_routes import router as agent_compare_router
 from compliance.api.agent_doc_check_routes import router as agent_doc_check_router
 from compliance.api.agent_compliance_check_routes import router as agent_compliance_check_router
+from compliance.api.snapshot_check_routes import router as snapshot_check_router
 from compliance.api.agent_findings_routes import router as agent_findings_router
 from compliance.api.saving_scan_routes import router as saving_scan_router
 from compliance.api.agent_migration_routes import router as agent_migration_router
@@ -160,6 +161,7 @@ app.include_router(agent_recurring_router, prefix="/api")
 app.include_router(agent_compare_router, prefix="/api")
 app.include_router(agent_doc_check_router, prefix="/api")
 app.include_router(agent_compliance_check_router, prefix="/api")
+app.include_router(snapshot_check_router, prefix="/api")
 app.include_router(agent_findings_router, prefix="/api")
 app.include_router(saving_scan_router, prefix="/api")
 app.include_router(agent_migration_router, prefix="/api")