feat: backend production readiness audit and fixes

[onelrian]

Backend Production Readiness Audit & Fixes

1. Objectives Accomplished

We successfully audited and improved the backend for production readiness, focusing on:

• Configuration Management: Eliminated hardcoded values.
• Observability: Replaced println! with structured logging (tracing).
• Reliability: Replaced panic!-prone code with robust error handling (anyhow).
• Build Stability: Fixed Dockerfile missing dependencies.

2. Changes Implemented

Configuration

• New Crate: config
• Files:
  • src/config.rs: Centralized Settings struct.
  • config/default.toml: Default values for work assignments.
• Outcome: The app now loads config from files and environment variables (APP_DATABASE_URL, RUN_MODE).

Structured Logging

• New Crates: tracing, tracing-subscriber
• Implementation:
  • Initialized subscriber in main.rs.
  • Replaced println! with info!, warn!, error! throughout main.rs and output.rs.
• Outcome: Logs are now structured, timestamped (if configured), and filterable via RUST_LOG.

Error Handling

• New Crates: anyhow, thiserror
• Implementation:
  • main now returns anyhow::Result<()>.
  • Refactored db.rs and group.rs to propagate errors instead of panicking (expect/unwrap removed in critical paths).
  • distribute_work returns anyhow::Result.
• Outcome: The application gracefully handles errors and provides context, rather than crashing unexpectedly.

Docker Build Fixes

• Issue: Missing libpq-dev caused build failures for diesel with postgres.
• Fix: Added libpq-dev to the builder stage in Dockerfile.
• Verification: docker build -t vividshift-backend . succeeded.

3. Verification

• Docker Build: Passed.
• Manual Code Review: Completed.