[Semantic Code Search] Add semantic_code_search MCP tool to Duo Chat on Web

Context

Currently, the Gitlab MCP Server tools are not available on Web Duo Chat.

The !206445 (merged) MR makes Web Duo Chat a client of the Gitlab MCP Server. This is behind the mcp_client FF which is still set to false by default. Additionally, the list of available tools is narrowed down to only get_issue.

References

• slack conversation / explanation
• MR introducing mcp_client FF: Implement MCP client that uses Gitlab MCP server (!206445 - merged)

Proposal

Add semantic_code_search to the list of tools available to Web Duo Chat.