fix: strengthen environment validation and remove empty string fallbacks

[akashgoudsidduluri]

Summary

This PR improves environment validation by ensuring that a valid Supabase URL and Anon/Publishable Key are present before the application starts.

Changes

• Added schema refinement to require:
  • at least one Supabase URL
  • at least one Supabase Anon/Publishable Key
• Removed empty string fallbacks from exported Supabase configuration values
• Preserved support for both VITE_* and NEXT_PUBLIC_* environment variable prefixes

Benefits

• Improves type safety
• Fails fast when required configuration is missing
• Avoids silently exporting empty strings for critical Supabase configuration

Fixes #639

[vercel]

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[akashgoudsidduluri]

Hey @durdana3105 can you review this PR.

[durdana3105]

Hey @durdana3105 can you review this PR.

please resolve the merge conflicts

[akashgoudsidduluri]

Hey @durdana3105 i have resolved the conflicts, you can review it.