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/pyproject.toml

@@ -18,7 +18,6 @@ dependencies = [
     "google-api-python-client>=2.156.0",
     "google-auth-oauthlib>=1.2.1",
     "kokoro>=0.9.4",
-    "linkup-sdk>=0.2.4",
     "llama-cloud-services>=0.6.25",
     "Markdown>=3.7",
     "markdownify>=0.14.1",
@@ -34,7 +33,6 @@ dependencies = [
     "spacy>=3.8.7",
     "en-core-web-sm@https://github.com/explosion/spacy-models/releases/download/en_core_web_sm-3.8.0/en_core_web_sm-3.8.0-py3-none-any.whl",
     "static-ffmpeg>=2.13",
-    "tavily-python>=0.3.2",
     "uvicorn[standard]>=0.34.0",
     "validators>=0.34.0",
     "youtube-transcript-api>=1.0.3",