refactor(config): consolidate origin validation

[thomasorgeval]

Summary

• Consolidates config origin parsing/HTTPS validation into one helper shared by trusted origins and APP_PUBLIC_URL.
• Keeps the existing accepted origins and validation messages behavior unchanged.

Expected impact

• Reduces duplicated URL parsing and local-HTTP exception checks in config validation.
• Makes future origin validation changes less error-prone and easier to review.

Verification

• pnpm nx test config
• pnpm nx typecheck config
• pnpm nx lint config
• pnpm format:check -- packages/config/src/index.ts
• git diff --check