Skip empty sst bind env values to preserve local config (Turbopack fix)

[TobiasMaehl-pIX]

• Problem: sst bind overwrites local env vars with empty strings from stack metadata. With Next.js Turbopack this can break client hydration.
• Fix: Filter out empty/undefined env values before merging into process env when running bound commands.
• Impact: Local dev works with sst bind + Turbopack, no change to non-empty envs.

[netlify]

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[FlanaganSe]

I think sst bind overwrites all local variables, not just those that are empty. You may not have noticed because many of them probably contained the same values.

This is only an issue if you're trying to develop locally with the same stage name as what is already deployed.
If you use a different stage name your local .env values won't be overwritten