feat(agents): consolidate connectors under mcp_discovery; route web search through google_search

MCP consolidation:
- Route all MCP-capable connectors (Slack, Jira, Linear, ClickUp, Airtable,
  Notion, Confluence, interim Gmail/Calendar, custom MCP) through a single
  `mcp_discovery` subagent. Drive/OneDrive/Dropbox stay native to enrich the KB.
- Deprecate Discord/Teams/Luma: no viable official MCP server.

Google-only web search:
- Remove the main-agent `web_search` tool and the SearXNG platform service;
  all public web search now flows through the `google_search` subagent via task().
- Deprecate the Tavily/SearXNG/Linkup/Baidu search connectors (HTTP 410 on
  create, "Deprecated" badge); guide heavy users to the custom MCP connector.
- Remove web search from anonymous chat (pure Q&A).
- Tear SearXNG out of docker compose + install scripts; drop tavily-python
  and linkup-sdk deps and their config/env vars.

Fix:
- metrics._package_version() now swallows any metadata lookup failure. A
  malformed editable-install distribution with no `Version` field raised
  KeyError deep in importlib.metadata, and since it runs on every
  record_subagent_invoke_duration call it was crashing every task()
  delegation. Verified end-to-end against live GPT-5.4.

Co-authored-by: Cursor <cursoragent@cursor.com>

surfsense_backend/tests/integration/agents/multi_agent_chat/test_web_search_delegation.py

@@ -0,0 +1,86 @@
+"""Backend E2E: public web search now flows through the ``google_search`` route.
+
+After the Google-only consolidation the main agent has no ``web_search`` tool;
+a web query must be delegated to the ``google_search`` subagent via ``task``.
+This drives the *assembled* production graph (real DB, scripted LLM) end to end:
+main agent emits a ``task(google_search, ...)`` call, the subagent runs a turn,
+and the main agent resumes to a final answer. Proves the delegation path the
+teardown relies on actually executes -- not just that the constants changed.
+"""
+
+from __future__ import annotations
+
+import pytest
+from langchain_core.messages import AIMessage, HumanMessage, ToolMessage
+from langgraph.checkpoint.memory import InMemorySaver
+
+from app.agents.chat.multi_agent_chat import create_multi_agent_chat_deep_agent
+from app.services.connector_service import ConnectorService
+from tests.integration.harness import ScriptedTurn, build_scripted_harness
+
+pytestmark = pytest.mark.integration
+
+
+def _last_ai_text(messages: list) -> str | None:
+    for m in reversed(messages):
+        if isinstance(m, AIMessage) and isinstance(m.content, str) and m.content:
+            return m.content
+    return None
+
+
+@pytest.mark.asyncio
+async def test_web_query_delegates_to_google_search(
+    db_session, db_user, db_workspace
+):
+    """A web-search query routes through ``task(google_search)`` and resumes.
+
+    Scripted sequence (the fake model is shared and consumed in order across the
+    main agent and the delegated subagent):
+      1. main agent  -> task(subagent_type="google_search")
+      2. subagent    -> plain text (never touches the scrape tool, so no network)
+      3. main agent  -> final answer
+    """
+    harness = build_scripted_harness(
+        turns=[
+            ScriptedTurn(
+                tool_calls=[
+                    {
+                        "name": "task",
+                        "args": {
+                            "subagent_type": "google_search",
+                            "description": "latest SurfSense release notes",
+                        },
+                        "id": "call_ws_task",
+                    }
+                ]
+            ),
+            ScriptedTurn(text="SERP: SurfSense v2 shipped Google-only web search."),
+            ScriptedTurn(text="SurfSense v2 shipped Google-only web search."),
+        ]
+    )
+
+    agent = await create_multi_agent_chat_deep_agent(
+        llm=harness.model,
+        workspace_id=db_workspace.id,
+        db_session=db_session,
+        connector_service=ConnectorService(db_session),
+        checkpointer=InMemorySaver(),
+        user_id=str(db_user.id),
+        thread_id=db_workspace.id,
+        agent_config=None,
+    )
+
+    result = await agent.ainvoke(
+        {"messages": [HumanMessage(content="search the web for SurfSense news")]},
+        config={"configurable": {"thread_id": "ws-google-delegation-1"}},
+    )
+
+    task_tool_messages = [
+        m
+        for m in result["messages"]
+        if isinstance(m, ToolMessage) and m.name == "task"
+    ]
+    assert task_tool_messages, "web query did not delegate through the task tool"
+    assert _last_ai_text(result["messages"]) == (
+        "SurfSense v2 shipped Google-only web search."
+    )