Phase 1d: AppState and config loader integration (refs #3)

Description

Implement AppState structure and config loader integration as part of Phase 1 database integration for issue #3.

Acceptance Criteria

• Create AppState struct with Database field
• Integrate Config::from_env() loader in main.rs
• Add proper error handling for configuration loading
• Initialize tracing before config loading
• Implement graceful application startup sequence
• Add AppState to Axum router with .with_state()
• Ensure all handlers can access database through State
• Add comprehensive logging for startup process
• Handle configuration errors with proper exit codes
• Test configuration loading with and without .env file

Technical Requirements

• Use Config::from_env() for environment variable loading
• Implement proper error propagation with anyhow::Result
• Add tracing logs for configuration and database initialization steps
• Structure AppState to be easily extensible for future services
• Follow Rust best practices for state management in web applications

Done Criteria

• AppState struct is properly defined and used
• Configuration loading works in both development and production environments
• All HTTP handlers can access database through AppState
• Startup sequence is logged with clear success/failure messages
• Tests pass for configuration loading scenarios
• Application exits gracefully on configuration errors

Related

• Parent: #3 (Implement database integration)
• Dependencies: #4 (sqlx driver), #5 (docker-compose), #6 (health endpoint)
• Part of: Phase 1 database integration implementation

Start by reading main.rs and the Config::from_env() entry point, then trace the HTTP handlers and their current router setup. Implement the AppState-based startup and configuration flow, including logging and error handling; done means handlers access the database state and configuration tests cover environments with and without a .env file.