refactor(agents): move utils + document_xml to app/agents/shared (slice 5a)

Two pure leaf modules with no intra-new_chat deps and no frozen importer.
Moving them now (before the middleware package) pre-empts two shared->new_chat
back-edges that the middleware move would otherwise create
(knowledge_search->utils, kb_postgres_backend->document_xml).

surfsense_backend/app/agents/new_chat/middleware/kb_postgres_backend.py

@@ -42,7 +42,7 @@ from langchain.tools import ToolRuntime
 from sqlalchemy import select
 from sqlalchemy.ext.asyncio import AsyncSession
 
-from app.agents.new_chat.document_xml import build_document_xml
+from app.agents.shared.document_xml import build_document_xml
 from app.agents.shared.path_resolver import (
     DOCUMENTS_ROOT,
     build_path_index,

surfsense_backend/app/agents/new_chat/middleware/knowledge_search.py

@@ -49,7 +49,7 @@ from app.agents.shared.path_resolver import (
     build_path_index,
     doc_to_virtual_path,
 )
-from app.agents.new_chat.utils import parse_date_or_datetime, resolve_date_range
+from app.agents.shared.utils import parse_date_or_datetime, resolve_date_range
 from app.db import (
     NATIVE_TO_LEGACY_DOCTYPE,
     Chunk,

surfsense_backend/app/agents/new_chat/tools/knowledge_base.py

@@ -692,7 +692,7 @@ async def search_knowledge_base_raw_async(
     # Preserve the public signature for compatibility even if values are unused.
     _ = (db_session, connector_service)
 
-    from app.agents.new_chat.utils import resolve_date_range
+    from app.agents.shared.utils import resolve_date_range
 
     resolved_start_date, resolved_end_date = resolve_date_range(
         start_date=start_date,

surfsense_backend/tests/unit/middleware/test_knowledge_search.py

@@ -5,7 +5,7 @@ import json
 import pytest
 from langchain_core.messages import AIMessage, HumanMessage
 
-from app.agents.new_chat.document_xml import build_document_xml as _build_document_xml
+from app.agents.shared.document_xml import build_document_xml as _build_document_xml
 from app.agents.new_chat.middleware.knowledge_search import (
     KBSearchPlan,
     KnowledgeBaseSearchMiddleware,