[TheAlexLichter]

Simplifies environment handling by making .env the only local development source and moving production configuration to remote secrets.

• Removes .env.example generation and the .secret()/.public() schema modifiers
• Updates deploy validation to reject server environment keys baked into plaintext Worker variables while allowing client VITE_* values from build inputs or schema defaults.
• Improves schema consistency across Vite, runtime, CLI, and HMR by using shared environment helpers and a process global registry.
• Refreshes CLI guidance, documentation, playground configuration, and relevant tests to reflect the new environment model.

[cpojer]

Thanks, I'm rebasing on main and cherry-picking.