[Bug]: deno task build Fresh (with Build step) won't read environment variables set in Deno Deploy project settings

### Problem description

If I use the "automatic" settings, it loads all the way through (seemingly not erroring on env vars), but then I can't use deno task build for tailwindcss.

Using deno task build for a Fresh deployment errors on the build step:

```
error: Uncaught (in promise) Error: SUPABASE_URL and SUPABASE_ANON_KEY are required.
throw new Error("SUPABASE_URL and SUPABASE_ANON_KEY are required.");
^
at file:///home/runner/work/mast/mast/utils/supabaseClient.ts:8:9
Error: Process completed with exit code 1.
```

### Steps to reproduce

1. Deploy a Fresh (with Build step) project to Deno Deploy
2. Add environment variables to Deno Deploy project level settings
3.

### Expected behavior

I would expect it to grab the environment variables successfully and deploy the project

### Environment

Deno2.0.0
Deno Deploy

### Possible solution

_No response_

### Additional context

_No response_

Start by reproducing the Deno Deploy Fresh deployment with a Build step and the environment variables referenced in utils/supabaseClient.ts, using deno task build. Trace whether project-level variables are available during that build; done means the build can read SUPABASE_URL and SUPABASE_ANON_KEY and the deployment completes successfully.

Written by the indexing model from the issue text.