swa deploy exits 0 without uploading files — StaticSitesClient receives unrecognized --environment flag

## Describe the bug

`swa deploy ./dist --deployment-token --env default` reports "Preparing deployment. Please wait..." then exits with code 0 - but **no files are uploaded** to the Static Web App.

## Root cause (from investigation)

The SWA CLI passes `--environment` to the underlying StaticSitesClient binary, but that binary only recognizes `--environmentName`. When StaticSitesClient receives the unrecognized flag, it prints its help text to stderr and exits 0, which the CLI interprets as success.

Evidence from running StaticSitesClient directly:

```
StaticSitesClient --app dist --apiToken --environment default --skipAppBuild true
ERROR(S):
Option 'environment' is unknown.
```

Exit code: **0** (not 1), so the CLI's `if (exitCode !== 0)` check passes.

## To Reproduce

1. Have a built static site in `./dist`
2. Run: `swa deploy ./dist --deployment-token --env default`
3. Observe output stops at "Preparing deployment. Please wait..."
4. No "Deployment Complete" message, no upload progress
5. Exit code is 0
6. Verify on Azure Portal or via curl that old files are still being served

## Expected behavior

- Either pass the correct `--environmentName` flag to StaticSitesClient
- Or detect the silent failure (no "Deployment Complete" in StaticSitesClient output) and report an error

## Workaround

Call StaticSitesClient directly with the correct flags:

```bash
StaticSitesClient --deploymentaction upload \
--app "dist" \
--appArtifactLocation "." \
--apiToken \
--skipAppBuild true \
--skipApiBuild true \
--deploymentProvider Custom
```

## Environment

- SWA CLI version: 2.0.8
- Node.js: v24.12.0 (also reproduced with v20.11.0)
- OS: Windows 11
- StaticSitesClient version: 1.0.0+689a6c1fe8fc32f40348cc41223a7e9d83dd43d2

## Related issues

- #783 (CLI doesn't produce a failure exit code in case of failure)
- #914 (SWA obscures underlying errors reported by StaticSitesClient)

Commencez par le point d’entrée du déploiement de SWA CLI qui invoque StaticSitesClient et recherchez l’argument `--environment` ; comparez-le au comportement de `--environmentName` décrit ici. Reproduisez le problème avec `swa deploy ./dist --deployment-token --env default`, puis vérifiez que le déploiement téléverse des fichiers, signale sa fin et ne traite pas le cas d’un indicateur non reconnu comme un succès.

Rédigé par le modèle d'indexation à partir du texte de l'issue.