The `aval` compiler's cross-platform compatibility and core compilation process.

## Summary

Every `avl compile` invocation fails on Windows with a generic `IO_FAILED` error at the publication step. The root cause is `syncDirectory()` in the compiler, which opens a **directory** with `fs.open(path, "r")` and calls `handle.sync()` — a POSIX-only durability pattern. On Windows, opening a directory handle this way is not supported, so publication always throws, the rollback path (which also calls `syncDirectory()`) fails too, and the real error gets swallowed into an `AggregateError` that the CLI never prints.

As far as I can tell, this makes the compiler unusable for all Windows users in v1.0.

## Environment

- Windows 11 Pro (build 10.0.26200)
- Node.js v24.13.0
- FFmpeg / FFprobe 8.0.1 (gyan.dev essentials build), on PATH
- Repo cloned from `main` on 2026-07-15

## Steps to reproduce

```sh
git clone github.com/pixel-point/aval....
cd aval
npm install
npm run build:public-packages
cd examples/grass-rabbit
node ../../packages/compiler/dist/cli.js compile motion.json --out public/rabbit-local.avl
```

## Actual result

Fails immediately (before any FFmpeg work is visible):

```
ERROR IO_FAILED — ...\examples\grass-rabbit\public\rabbit-local.avl — Publication failed and the previous output pair could not be restored
```

Same result with `--force`, with a fresh output filename, and with absolute `--ffmpeg`/`--ffprobe` paths.

## Root cause

`packages/compiler/src/compile/output.ts`:

```ts
export async function syncDirectory(path: string): Promise