Add environment-specific configuration template

[PAMulligan]

Description

Add an environment configuration utility to the generated project templates. This provides type-safe environment variable loading with validation, replacing raw `process.env` access.

Why

Raw `process.env` access is untyped and error-prone — missing variables cause runtime crashes. A typed config utility catches missing/invalid variables at startup with clear error messages.

Acceptance Criteria

• Add a `src/config.ts` template to `setup-project.sh`

• Use Zod for environment variable validation:
  ```typescript
  import { z } from 'zod';

  const envSchema = z.object({
  NODE_ENV: z.enum(['development', 'production', 'test']).default('development'),
  PORT: z.coerce.number().default(3000),
  DATABASE_URL: z.string().url(),
  JWT_SECRET: z.string().min(32),
  LOG_LEVEL: z.enum(['debug', 'info', 'warn', 'error']).default('info'),
  });

  export const config = envSchema.parse(process.env);
  export type Config = z.infer;
  ```

• Import and use `config` in the generated `src/index.ts` instead of raw `process.env`

• Provide different defaults for development vs. production

• For Cloudflare Workers, adapt to use Hono's `Bindings` pattern instead

• CI passes