refactor(config): enforce strict runtime validation for environment variables

[0dillon]

Summary

Currently, our application consumes environment variables using loose type casting (e.g., process.env.SECRET as string). This is a massive operational risk. If a required variable is missing or malformed during deployment, the API might start up successfully but crash unexpectedly during runtime when that specific configuration is accessed.

We need to implement a 'fail-fast' architecture at startup. By migrating our configuration logic to a strict Zod schema, we can validate the presence, type, and format of every environment variable the moment the Node process initializes. If the environment is invalid, the process must terminate immediately with a detailed error log.

Acceptance Criteria

• Define a comprehensive Zod schema for all configuration variables.
• Implement initialization logic to parse and validate process.env on startup.
• Remove all unsafe type assertions from the codebase.
• Ensure the process exits with code 1 if validation fails.

Tech Stack

TypeScript (Node.js 24), Zod.