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/app/observability/metrics.py

@@ -36,7 +36,11 @@ _ERROR_CATEGORY_HINTS: tuple[tuple[str, tuple[str, ...]], ...] = (
 
 
 def _package_version() -> str:
-    with contextlib.suppress(metadata.PackageNotFoundError):
+    # Best-effort telemetry tag only: never let a version lookup crash the
+    # request path. Besides PackageNotFoundError, a malformed/dynamic editable
+    # install can have distribution metadata with no "Version" field, which
+    # raises KeyError deep in importlib.metadata. Suppress broadly.
+    with contextlib.suppress(Exception):
         return metadata.version("surf-new-backend")
     return "unknown"