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_web/content/docs/connectors/baidu-search.mdx

@@ -1,10 +1,14 @@
 ---
-title: Baidu Search
-description: Search the Chinese web with Baidu AI Search in SurfSense
+title: Baidu Search (Deprecated)
+description: The Baidu Search connector is deprecated; public web search now runs through Google Search
 ---
 
 # Baidu Search Integration Setup Guide
 
+<Callout type="warn" title="Deprecated">
+The Baidu Search connector is **deprecated** and can no longer be connected (the backend refuses new connections with HTTP 410). Public web search in SurfSense now runs through the built-in **Google Search** specialist — see [Web Search](/docs/how-to/web-search). Existing Baidu connector rows remain manageable, and you can add an alternative provider through a Custom MCP connector. The guide below is retained for reference only.
+</Callout>
+
 This guide walks you through connecting Baidu AI Search to SurfSense for Chinese web search and AI-powered research.
 
 ## How it works