refactor(agents): group MCP tools into shared/tools/mcp/ subpackage

The three MCP siblings (mcp_client/mcp_tool/mcp_tools_cache) served one
objective but sat loose at the top of shared/tools. Grouped them into an
mcp/ package and dropped the redundant prefix: client.py, tool.py, cache.py.
Updated all importers (routes, mcp_tools subagent, e2e fake patch targets,
unit test) to the new paths.

surfsense_backend/tests/e2e/fakes/mcp_runtime.py

@@ -137,10 +137,10 @@ def install(active_patches: list[Any]) -> None:
     """Patch production MCP streamable-HTTP boundaries exactly once."""
     targets = [
         (
-            "app.agents.shared.tools.mcp_tool.streamablehttp_client",
+            "app.agents.shared.tools.mcp.tool.streamablehttp_client",
             _fake_streamablehttp_client,
         ),
-        ("app.agents.shared.tools.mcp_tool.ClientSession", _FakeClientSession),
+        ("app.agents.shared.tools.mcp.tool.ClientSession", _FakeClientSession),
     ]
     for target, replacement in targets:
         p = patch(target, replacement)

surfsense_backend/tests/unit/agents/new_chat/tools/test_mcp_tools_cache.py

@@ -7,7 +7,7 @@ from types import SimpleNamespace
 
 import pytest
 
-from app.agents.shared.tools.mcp_tools_cache import (
+from app.agents.shared.tools.mcp.cache import (
     CachedMCPToolDef,
     CachedMCPTools,
     read_cached_tools,