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/e2e/run_backend.py

@@ -282,6 +282,7 @@ def _install_runtime_fakes() -> None:
         mcp_oauth_runtime as _fake_mcp_oauth_runtime,
         mcp_runtime as _fake_mcp_runtime,
         native_google as _fake_native_google,
+        notion_mcp_module as _fake_notion_mcp_module,
         notion_module as _fake_notion_module,
         onedrive_graph as _fake_onedrive_graph,
         slack_module as _fake_slack_module,
@@ -295,6 +296,7 @@ def _install_runtime_fakes() -> None:
     _fake_onedrive_graph.install(_active_patches)
     _fake_dropbox_api.install(_active_patches)
     _fake_notion_module.install(_active_patches)
+    _fake_notion_mcp_module.install(_active_patches)
     _fake_linear_module.install(_active_patches)
     _fake_jira_module.install(_active_patches)
     _fake_clickup_module.install(_active_patches)