fix: mcp_tools URL-only config triggers unnecessary discover-all in entry.rs

[kordless]

In src/entry.rs install_mcp_servers(), when mcp_tools contains only URLs (no file tools), file_tools is empty which triggers the fallback that discovers and copies all image tools. The fallback should only fire when mcp_tools itself is empty, not when the file-tool subset is empty. Fix: change condition from file_tools.is_empty() to ws_config.mcp_tools.is_empty(). Same issue exists in write_provider_config(). Raised in code review with Codex.