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/unit/tasks/chat/streaming/test_task_span.py

@@ -28,7 +28,7 @@ def test_clear_ignored_for_non_task_tool() -> None:
     open_task_span(state, run_id="run-1")
     sid = state.active_span_id
     clear_task_span_if_delegating_task_ended(
-        state, tool_name="web_search", run_id="run-1"
+        state, tool_name="scrape_webpage", run_id="run-1"
     )
     assert state.active_span_id == sid
     assert state.active_task_run_id == "run-1"

surfsense_backend/tests/unit/tasks/chat/test_content_builder.py

@@ -128,14 +128,14 @@ class TestToolHeavyTurn:
 
         b.on_tool_input_start(
             ui_id="call_run123",
-            tool_name="web_search",
+            tool_name="scrape_webpage",
             langchain_tool_call_id="lc_tool_abc",
         )
         b.on_tool_input_delta("call_run123", '{"query":')
         b.on_tool_input_delta("call_run123", '"surfsense"}')
         b.on_tool_input_available(
             ui_id="call_run123",
-            tool_name="web_search",
+            tool_name="scrape_webpage",
             args={"query": "surfsense"},
             langchain_tool_call_id="lc_tool_abc",
         )
@@ -150,7 +150,7 @@ class TestToolHeavyTurn:
         tool_part = snap[1]
         assert tool_part["type"] == "tool-call"
         assert tool_part["toolCallId"] == "call_run123"
-        assert tool_part["toolName"] == "web_search"
+        assert tool_part["toolName"] == "scrape_webpage"
         assert tool_part["args"] == {"query": "surfsense"}
         # ``argsText`` is the pretty-printed final JSON, not the raw
         # streaming buffer (FE ``stream-pipeline.ts:128``).