Changed koffi import from top-level to dynamic require in enableWindowsVTInput() and added --external koffi to bun build. This prevents embedding all 18 platform .node files (~74MB) into every compiled binary. For Windows builds, only the win32_x64 koffi.node is shipped alongside the binary. Binary size reduction: darwin-arm64 142MB -> 67MB, archive 43MB -> 28MB.