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>

docker/scripts/install.ps1

@@ -329,7 +329,6 @@ Write-Step "Downloading SurfSense files"
 Write-Info "Installation directory: $InstallDir"
 
 New-Item -ItemType Directory -Path "$InstallDir\scripts" -Force | Out-Null
-New-Item -ItemType Directory -Path "$InstallDir\searxng" -Force | Out-Null
 New-Item -ItemType Directory -Path "$InstallDir\proxy" -Force | Out-Null
 
 $Files = @(
@@ -339,8 +338,6 @@ $Files = @(
     @{ Src = "docker/proxy/Caddyfile";                   Dest = "proxy/Caddyfile" }
     @{ Src = "docker/postgresql.conf";                   Dest = "postgresql.conf" }
     @{ Src = "docker/scripts/migrate-database.ps1";      Dest = "scripts/migrate-database.ps1" }
-    @{ Src = "docker/searxng/settings.yml";              Dest = "searxng/settings.yml" }
-    @{ Src = "docker/searxng/limiter.toml";              Dest = "searxng/limiter.toml" }
 )
 
 foreach ($f in $Files) {