This fixes the Windows build failure discussed in https://github.com/ghostty-org/ghostty/discussions/10148 When building on Windows, `symbols-unigen` and `props-unigen` crash with `error.FileTooBig` because `stdout.end()` calls `setEndPos()` to truncate the output. Windows does not support `SetEndOfFile` on pipes or console handles - it returns `ERROR_INVALID_PARAMETER`, which Zig maps to `error.FileTooBig`. Using `flush()` instead of `end()` is correct here because: 1. `end()` flushes AND truncates - useful when overwriting files that might have leftover content 2. For stdout captured as a pipe, there's nothing to truncate - we're writing sequentially to a fresh pipe 3. `flush()` ensures all buffered data is sent, which is all that's needed CI before fix was failing with FileTooBig, after fix builds successfully: https://github.com/remorses/opentui/actions/runs/20671299561/job/59352503875