feat(B-SENS): Sensitive Data Boundary + AI/Data Exposure Policy + AIProvider Compliance

B-SENS: app/core/sensitive_data.py (NEU) — zentrale Sensitive-Field-Verwaltung
- SENSITIVE_FIELDS dict für contact/user/mail_account/system_settings
- is_sensitive(), sanitize_dict(), register_sensitive_fields()
- Integration: errors.py (Log-Redaction), audit.py (Audit-Masking), export_service.py (Export-Filter), embedding.py (Index-Filter)

B-DATA-POL: AI/Data Exposure Policy
- DATA_EXPOSURE_POLICY: pro Entity+Field welche Systeme erlaubt (llm_context/search/embeddings/rag/agent_memory/export)
- filter_for_llm_context/search/embeddings/export/rag/agent_memory()

B-AIPROV-COMP: AIProvider Compliance Metadata
- Migration 0119: 7 neue Spalten an ai_providers (region, hosting_type, dpa_status, retention_policy, training_on_customer_data, transfer_notice, allowed_data_classes)
- llm_client.py: get_provider_compliance() + check_data_class_allowed()

B-PRIV-TEST: 76 Tests in test_sensitive_data.py — alle grün
- Sensitive Fields, Exposure Policy, Provider Compliance, Secrets-always-blocked
- Keine Regression: 39 LLM-Client Tests grün

app/core/audit.py

@@ -21,14 +21,21 @@ async def log_audit(
     changes: dict[str, Any] | None = None,
     details: dict[str, Any] | None = None,
 ) -> AuditLog:
-    """Create an audit log entry."""
+    """Create an audit log entry.
+
+    Sensitive fields in *changes* are masked using the central
+    :mod:`app.core.sensitive_data` module.
+    """
+    from app.core.sensitive_data import sanitize_dict
+
+    masked_changes = sanitize_dict(changes, entity_type) if changes else changes
     entry = AuditLog(
         tenant_id=tenant_id,
         user_id=user_id,
         action=action,
         entity_type=entity_type,
         entity_id=entity_id,
-        changes=changes,
+        changes=masked_changes,
     )
     db.add(entry)
     await db.flush()
@@ -46,14 +53,19 @@ async def log_deletion(
     """Create a deletion history entry (merged from DeletionLog into EntityHistory).
 
     Stores the full entity snapshot in snapshot_before for forensic recovery.
+    Sensitive fields are masked using the central
+    :mod:`app.core.sensitive_data` module.
     """
+    from app.core.sensitive_data import sanitize_dict
+
+    masked_snapshot = sanitize_dict(entity_snapshot, entity_type)
     entry = EntityHistory(
         tenant_id=tenant_id,
         user_id=user_id,
         entity_type=entity_type,
         entity_id=entity_id,
         action="delete",
-        snapshot_before=entity_snapshot,
+        snapshot_before=masked_snapshot,
         snapshot_after=None,
         changes=None,
         owner_id=user_id,