GitHub Actions deploy step is broken and duplicates Vercel's Git integration #11

Describe the bug

With the build itself fixed, the workflow's deploy step (`amondnet/vercel-action@v25`) fails on its own:

```
Vercel CLI 25.1.0
Deploying ephbaums-projects/ephbaumdotdev
Error! Your Vercel CLI version is outdated. This endpoint requires version 47.2.2 or later.
```

`amondnet/vercel-action@v25` pins Vercel CLI 25.1.0 and is unmaintained. Separately, this step is redundant: Vercel's Git integration is already connected directly to this repo and builds/deploys `main` on every push, so a passing deploy step here would just publish the same commit a second time through a second path.

Expected behavior

The workflow shouldn't attempt to deploy at all — Vercel's Git integration already owns that. The workflow should be a build gate only.

Additional context

`VERCEL_TOKEN` / `VERCEL_ORG_ID` / `VERCEL_PROJECT_ID` repo secrets become unused once this step is removed and can be revoked. Fixed in #9.