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/unit/utils/test_validators.py

@@ -4,6 +4,7 @@ import pytest
 from fastapi import HTTPException
 
 from app.utils.validators import (
+    raise_if_connector_deprecated,
     validate_connector_config,
     validate_connectors,
     validate_document_ids,
@@ -331,3 +332,31 @@ def test_validate_connector_config_invalid():
     # Invalid URL format in SEARXNG_API
     with pytest.raises(ValueError):
         validate_connector_config("SEARXNG_API", {"SEARXNG_HOST": "not-a-url"})
+
+
+@pytest.mark.parametrize(
+    "connector_type",
+    [
+        "DISCORD_CONNECTOR",
+        "TEAMS_CONNECTOR",
+        "LUMA_CONNECTOR",
+        "TAVILY_API",
+        "SEARXNG_API",
+        "LINKUP_API",
+        "BAIDU_SEARCH_API",
+    ],
+)
+def test_raise_if_connector_deprecated_blocks(connector_type):
+    """Deprecated connector types are refused with HTTP 410."""
+    with pytest.raises(HTTPException) as excinfo:
+        raise_if_connector_deprecated(connector_type)
+    assert excinfo.value.status_code == 410
+
+
+@pytest.mark.parametrize(
+    "connector_type",
+    ["SLACK_CONNECTOR", "NOTION_CONNECTOR", "SERPER_API", "MCP_CONNECTOR"],
+)
+def test_raise_if_connector_deprecated_allows_active(connector_type):
+    """Active connector types pass through without raising."""
+    raise_if_connector_deprecated(connector_type)