feat(sdk): vendor-compliance cross-module integration — VVT, obligations, TOM, loeschfristen

Integrate the vendor-compliance module with four DSGVO modules to eliminate
data silos and resolve the VVT processor tab's ephemeral state problem.

- Reposition vendor-compliance sidebar from seq 4200 to 2500 (after VVT)
- VVT: replace ephemeral ProcessorRecord state with Vendor-API fetch (read-only)
- Obligations: add linked_vendor_ids (JSONB) + compliance check #12 MISSING_VENDOR_LINK
- TOM: add vendor TOM-controls cross-reference table in overview tab
- Loeschfristen: add linked_vendor_ids (JSONB) + vendor picker + document section
- Migrations: 069_obligations_vendor_link.sql, 070_loeschfristen_vendor_link.sql
- Tests: 12 new backend tests (125 total pass)
- Docs: update obligations.md + vendors.md with cross-module integration

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend-compliance/tests/test_loeschfristen_routes.py

@@ -56,6 +56,7 @@ def make_policy_row(overrides=None):
         "responsible_person": None,
         "release_process": None,
         "linked_vvt_activity_ids": [],
+        "linked_vendor_ids": [],
         "status": "DRAFT",
         "last_review_date": None,
         "next_review_date": None,
@@ -132,7 +133,7 @@ class TestRowToDict:
 class TestJsonbFields:
     def test_jsonb_fields_set(self):
         expected = {"affected_groups", "data_categories", "legal_holds",
-                    "storage_locations", "linked_vvt_activity_ids", "tags"}
+                    "storage_locations", "linked_vvt_activity_ids", "linked_vendor_ids", "tags"}
         assert JSONB_FIELDS == expected
 
 
@@ -618,3 +619,68 @@ class TestDeleteLoeschfrist:
         )
         call_params = mock_db.execute.call_args[0][1]
         assert call_params["tenant_id"] == "9282a473-5c95-4b3a-bf78-0ecc0ec71d3e"
+
+
+# =============================================================================
+# Linked Vendor IDs (Vendor-Compliance Integration)
+# =============================================================================
+
+class TestLinkedVendorIds:
+    def test_create_with_linked_vendor_ids(self, mock_db):
+        row = make_policy_row({"linked_vendor_ids": ["vendor-1"]})
+        mock_db.execute.return_value.fetchone.return_value = row
+        resp = client.post("/loeschfristen", json={
+            "data_object_name": "Vendor-Daten",
+            "linked_vendor_ids": ["vendor-1"],
+        })
+        assert resp.status_code == 201
+        import json
+        call_params = mock_db.execute.call_args[0][1]
+        assert json.loads(call_params["linked_vendor_ids"]) == ["vendor-1"]
+
+    def test_create_without_linked_vendor_ids_defaults_empty(self, mock_db):
+        row = make_policy_row()
+        mock_db.execute.return_value.fetchone.return_value = row
+        resp = client.post("/loeschfristen", json={
+            "data_object_name": "Ohne Vendor",
+        })
+        assert resp.status_code == 201
+        import json
+        call_params = mock_db.execute.call_args[0][1]
+        assert json.loads(call_params["linked_vendor_ids"]) == []
+
+    def test_update_linked_vendor_ids(self, mock_db):
+        updated_row = make_policy_row({"linked_vendor_ids": ["v1"]})
+        mock_db.execute.return_value.fetchone.return_value = updated_row
+        resp = client.put(f"/loeschfristen/{POLICY_ID}", json={
+            "linked_vendor_ids": ["v1"],
+        })
+        assert resp.status_code == 200
+        import json
+        call_params = mock_db.execute.call_args[0][1]
+        assert json.loads(call_params["linked_vendor_ids"]) == ["v1"]
+
+    def test_update_clears_linked_vendor_ids(self, mock_db):
+        updated_row = make_policy_row({"linked_vendor_ids": []})
+        mock_db.execute.return_value.fetchone.return_value = updated_row
+        resp = client.put(f"/loeschfristen/{POLICY_ID}", json={
+            "linked_vendor_ids": [],
+        })
+        assert resp.status_code == 200
+        import json
+        call_params = mock_db.execute.call_args[0][1]
+        assert json.loads(call_params["linked_vendor_ids"]) == []
+
+    def test_schema_includes_linked_vendor_ids(self):
+        create_obj = LoeschfristCreate(
+            data_object_name="Test",
+            linked_vendor_ids=["vendor-a", "vendor-b"],
+        )
+        assert create_obj.linked_vendor_ids == ["vendor-a", "vendor-b"]
+
+        update_obj = LoeschfristUpdate(linked_vendor_ids=["vendor-c"])
+        data = update_obj.model_dump(exclude_unset=True)
+        assert data["linked_vendor_ids"] == ["vendor-c"]
+
+    def test_jsonb_fields_contains_linked_vendor_ids(self):
+        assert "linked_vendor_ids" in JSONB_FIELDS