refactor(agents): split dedup_tool_calls; move HITL middleware to main_agent

DedupHITLToolCallsMiddleware is only wired by the main_agent stack, but
its module also exports dedup-key resolvers consumed by the shared MCP
tool layer. Splitting keeps the resolvers (dedup_key_full_args,
wrap_dedup_key_by_arg_name, DedupResolver) in shared and moves the
middleware class verbatim into main_agent/middleware/dedup_hitl.py
(merged with its builder), eliminating the shared->main_agent dependency
that a flat move would create. No behavior change.

surfsense_backend/tests/unit/agents/new_chat/test_dedup_tool_calls.py

@@ -6,7 +6,7 @@ import pytest
 from langchain_core.messages import AIMessage
 from langchain_core.tools import StructuredTool
 
-from app.agents.shared.middleware.dedup_tool_calls import (
+from app.agents.multi_agent_chat.main_agent.middleware.dedup_hitl import (
     DedupHITLToolCallsMiddleware,
 )
 

surfsense_backend/tests/unit/middleware/test_dedup_hitl_tool_calls.py

@@ -2,8 +2,10 @@ import pytest
 from langchain_core.messages import AIMessage
 from langchain_core.tools import StructuredTool
 
-from app.agents.shared.middleware.dedup_tool_calls import (
+from app.agents.multi_agent_chat.main_agent.middleware.dedup_hitl import (
     DedupHITLToolCallsMiddleware,
+)
+from app.agents.shared.middleware.dedup_tool_calls import (
     wrap_dedup_key_by_arg_name,
 )