Add missing environment variable validation to env.validation.ts

[Hallab7]

Description

The .env.example file contains 20+ environment variables for rate limiting, retention, cron schedules, and salt versioning that are not validated in env.validation.ts. This allows invalid configuration to reach production.

Add complete Zod schema validation for all environment variables documented in .env.example including AUTH_RATE_LIMIT_, RETENTION_, cron expressions, and VERIFICATION_HASH_SALT_V* variables.

Acceptance criteria

• Every variable in .env.example has corresponding validation in env.validation.ts
• Invalid values fail fast at startup with clear error messages
• Cron expressions are validated with proper regex patterns
• Retention day values are bounded (1-3650 days)
• Rate limit windows and counts have sensible bounds

Testing requirements

• Validation catches invalid cron syntax
• Validation rejects out-of-range retention values
• npm run lint and npm run test pass

Files

src/config/env.validation.ts, .env.example, src/config/env.validation.spec.ts

Suggested branch

feat/complete-env-validation

Suggested commit message

feat(config): add comprehensive environment validation