[split-required] Split final 43 files (500-668 LOC) to complete refactoring

klausur-service (11 files):
- cv_gutter_repair, ocr_pipeline_regression, upload_api
- ocr_pipeline_sessions, smart_spell, nru_worksheet_generator
- ocr_pipeline_overlays, mail/aggregator, zeugnis_api
- cv_syllable_detect, self_rag

backend-lehrer (17 files):
- classroom_engine/suggestions, generators/quiz_generator
- worksheets_api, llm_gateway/comparison, state_engine_api
- classroom/models (→ 4 submodules), services/file_processor
- alerts_agent/api/wizard+digests+routes, content_generators/pdf
- classroom/routes/sessions, llm_gateway/inference
- classroom_engine/analytics, auth/keycloak_auth
- alerts_agent/processing/rule_engine, ai_processor/print_versions

agent-core (5 files):
- brain/memory_store, brain/knowledge_graph, brain/context_manager
- orchestrator/supervisor, sessions/session_manager

admin-lehrer (5 components):
- GridOverlay, StepGridReview, DevOpsPipelineSidebar
- DataFlowDiagram, sbom/wizard/page

website (2 files):
- DependencyMap, lehrer/abitur-archiv

Other: nibis_ingestion, grid_detection_service, export-doclayout-onnx

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

agent-core/sessions/__init__.py

@@ -8,11 +8,12 @@ Provides:
 - SessionState: Session state enumeration
 """
 
-from agent_core.sessions.session_manager import (
+from agent_core.sessions.session_models import (
     AgentSession,
-    SessionManager,
     SessionState,
+    SessionCheckpoint,
 )
+from agent_core.sessions.session_manager import SessionManager
 from agent_core.sessions.heartbeat import HeartbeatMonitor
 from agent_core.sessions.checkpoint import CheckpointManager
 
@@ -20,6 +21,7 @@ __all__ = [
     "AgentSession",
     "SessionManager",
     "SessionState",
+    "SessionCheckpoint",
     "HeartbeatMonitor",
     "CheckpointManager",
 ]