Audit codebase and improve production readiness

[qvidal01]

…hancements

Security Improvements:

• Add constant-time comparison for webhook secrets (prevents timing attacks)
• Replace MD5 with SHA256 for anonymous user key hashing
• Add subprocess timeout and parameter validation in generate_qart()
• Add file upload validation with MIME type detection and size limits
• Run Docker container as non-root user

New Modules:

• config.py: Centralized configuration with validation and type safety
• utils.py: File upload validation and temp file management utilities

Docker & Configuration:

• Fix version inconsistency (now 0.3.0 everywhere)
• Fix Docker port configuration (consistently 8000)
• Add production-ready docker-compose with health checks
• Add .env.example documenting all configuration options
• Add setuptools package discovery configuration

Documentation:

• ARCHITECTURE.md: System design, module structure, data flow diagrams
• INSTALL.md: Comprehensive installation guide for all platforms
• CHANGELOG.md: Version history following Keep a Changelog format

Testing:

• Add test_config.py: Tests for configuration module (17 tests)
• Add test_utils.py: Tests for utilities module (12 tests)
• All 62 tests passing

Dependencies:

• Add httpx to main dependencies (required for auth validation)
• Update Python requirement to >=3.10