`combine_archives` spawns `zig ar -M`, hard-coding the command name `"zig"` and relying on the binary being on `PATH`. On Windows when the build is driven by an absolute zig.exe path (common in CI and Scoop/winget installs), this surfaces as `error: FileNotFound`. Pass `b.graph.zig_exe` explicitly so the tool always uses the exact zig binary driving the build, matching how other build tools in this repo spawn zig subcommands. Part of the Win32 apprt upstreaming series (see discussion #2563 / mattn/ghostty#1).