refactor(agents): move feature flags to app/agents/shared/feature_flags (slice 2b)

Promote the agent feature-flag resolver (AgentFeatureFlags / get_flags) out of
`new_chat` into the cross-agent `app/agents/shared` kernel.

feature_flags is a pure leaf consumed across the multi-agent middleware stack,
the chat routes, and tests. Moved it via git mv (content unchanged) and flipped
all 37 importers to app.agents.shared.feature_flags. A thin re-export shim
remains at new_chat/feature_flags.py only for the not-yet-retired single-agent
(chat_deepagent); it goes away with the single-agent deletion.

Behavior-preserving: only import paths change. 1243 tests green.

surfsense_backend/tests/unit/agents/multi_agent_chat/middleware/shared/permissions/test_permission_ask_mcp_context.py

@@ -19,7 +19,7 @@ from app.agents.multi_agent_chat.middleware.shared.permissions import (
 from app.agents.multi_agent_chat.middleware.shared.permissions.ask.payload import (
     build_permission_ask_payload,
 )
-from app.agents.new_chat.feature_flags import AgentFeatureFlags
+from app.agents.shared.feature_flags import AgentFeatureFlags
 from app.agents.new_chat.permissions import Rule, Ruleset
 
 

surfsense_backend/tests/unit/agents/multi_agent_chat/middleware/shared/permissions/test_subagent_owned_ruleset.py

@@ -26,7 +26,7 @@ from typing_extensions import TypedDict
 from app.agents.multi_agent_chat.middleware.shared.permissions import (
     build_permission_mw,
 )
-from app.agents.new_chat.feature_flags import AgentFeatureFlags
+from app.agents.shared.feature_flags import AgentFeatureFlags
 from app.agents.new_chat.permissions import Rule, Ruleset
 
 

surfsense_backend/tests/unit/agents/multi_agent_chat/middleware/shared/permissions/test_trusted_tool_save_on_always.py

@@ -17,7 +17,7 @@ from typing_extensions import TypedDict
 from app.agents.multi_agent_chat.middleware.shared.permissions import (
     build_permission_mw,
 )
-from app.agents.new_chat.feature_flags import AgentFeatureFlags
+from app.agents.shared.feature_flags import AgentFeatureFlags
 from app.agents.new_chat.permissions import Rule, Ruleset
 
 

surfsense_backend/tests/unit/agents/multi_agent_chat/subagents/shared/test_subagent_builder.py

@@ -25,7 +25,7 @@ from app.agents.multi_agent_chat.middleware.shared.permissions.middleware.core i
 from app.agents.multi_agent_chat.subagents.shared.subagent_builder import (
     pack_subagent,
 )
-from app.agents.new_chat.feature_flags import AgentFeatureFlags
+from app.agents.shared.feature_flags import AgentFeatureFlags
 from app.agents.new_chat.permissions import Rule, Ruleset, evaluate
 
 

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

@@ -10,7 +10,7 @@ import pytest
 from langchain_core.messages import ToolMessage
 from langchain_core.tools import tool
 
-from app.agents.new_chat.feature_flags import AgentFeatureFlags
+from app.agents.shared.feature_flags import AgentFeatureFlags
 from app.agents.new_chat.middleware.action_log import ActionLogMiddleware
 from app.agents.new_chat.tools.registry import ToolDefinition
 

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

@@ -4,7 +4,7 @@ from __future__ import annotations
 
 import pytest
 
-from app.agents.new_chat.feature_flags import (
+from app.agents.shared.feature_flags import (
     AgentFeatureFlags,
     reload_for_tests,
 )

surfsense_backend/tests/unit/routes/test_revert_turn_route.py

@@ -18,7 +18,7 @@ from unittest.mock import AsyncMock, patch
 
 import pytest
 
-from app.agents.new_chat.feature_flags import AgentFeatureFlags
+from app.agents.shared.feature_flags import AgentFeatureFlags
 from app.routes import agent_revert_route
 from app.services.revert_service import RevertOutcome