[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>

klausur-service/backend/mail/aggregator_smtp.py

@@ -0,0 +1,131 @@
+"""
+Mail Aggregator SMTP — email sending via SMTP.
+
+Extracted from aggregator.py for modularity.
+"""
+
+import logging
+import smtplib
+from typing import Optional, List, Dict, Any
+from email.mime.text import MIMEText
+from email.mime.multipart import MIMEMultipart
+
+from .mail_db import get_email_account
+from .models import EmailComposeRequest, EmailSendResult
+
+logger = logging.getLogger(__name__)
+
+
+class SMTPConnectionError(Exception):
+    """Raised when SMTP connection fails."""
+    pass
+
+
+class SMTPMixin:
+    """SMTP-related methods for MailAggregator.
+
+    Provides SMTP connection testing and email sending.
+    Must be mixed into a class that has ``_credentials_service``.
+    """
+
+    async def test_smtp_connection(
+        self,
+        smtp_host: str,
+        smtp_port: int,
+        smtp_ssl: bool,
+        email_address: str,
+        password: str,
+    ) -> tuple:
+        """Test SMTP connection. Returns (success, error)."""
+        try:
+            if smtp_ssl:
+                smtp = smtplib.SMTP_SSL(smtp_host, smtp_port)
+            else:
+                smtp = smtplib.SMTP(smtp_host, smtp_port)
+                smtp.starttls()
+
+            smtp.login(email_address, password)
+            smtp.quit()
+            return True, None
+
+        except Exception as e:
+            logger.warning(f"SMTP test failed for {email_address}: {e}")
+            return False, f"SMTP Error: {str(e)}"
+
+    async def send_email(
+        self,
+        account_id: str,
+        user_id: str,
+        request: EmailComposeRequest,
+    ) -> EmailSendResult:
+        """
+        Send an email via SMTP.
+
+        Args:
+            account_id: The account to send from
+            user_id: The user ID
+            request: The compose request with recipients and content
+
+        Returns:
+            EmailSendResult with success status
+        """
+        account = await get_email_account(account_id, user_id)
+        if not account:
+            return EmailSendResult(success=False, error="Account not found")
+
+        # Verify the account_id matches
+        if request.account_id != account_id:
+            return EmailSendResult(success=False, error="Account mismatch")
+
+        # Get credentials
+        vault_path = account.get("vault_path", "")
+        creds = await self._credentials_service.get_credentials(account_id, vault_path)
+        if not creds:
+            return EmailSendResult(success=False, error="Credentials not found")
+
+        try:
+            # Create message
+            if request.is_html:
+                msg = MIMEMultipart("alternative")
+                msg.attach(MIMEText(request.body, "html"))
+            else:
+                msg = MIMEText(request.body, "plain")
+
+            msg["Subject"] = request.subject
+            msg["From"] = account["email"]
+            msg["To"] = ", ".join(request.to)
+
+            if request.cc:
+                msg["Cc"] = ", ".join(request.cc)
+
+            if request.reply_to_message_id:
+                msg["In-Reply-To"] = request.reply_to_message_id
+                msg["References"] = request.reply_to_message_id
+
+            # Send via SMTP
+            if account["smtp_ssl"]:
+                smtp = smtplib.SMTP_SSL(account["smtp_host"], account["smtp_port"])
+            else:
+                smtp = smtplib.SMTP(account["smtp_host"], account["smtp_port"])
+                smtp.starttls()
+
+            smtp.login(creds.email, creds.password)
+
+            # All recipients
+            all_recipients = list(request.to)
+            if request.cc:
+                all_recipients.extend(request.cc)
+            if request.bcc:
+                all_recipients.extend(request.bcc)
+
+            smtp.sendmail(account["email"], all_recipients, msg.as_string())
+            smtp.quit()
+
+            return EmailSendResult(
+                success=True,
+                message_id=msg.get("Message-ID"),
+            )
+
+        except Exception as e:
+            logger.error(f"Failed to send email: {e}")
+            return EmailSendResult(success=False, error=str(e))