feat: comprehensive DevEnv testing framework, CUDA support, and container implementation

[Maddonix]

• ✅ DevEnv Testing Framework: Complete with 6 test suites (quick, workflows, containers, e2e, ci, full)
• ✅ CUDA/PyTorch Integration: Successfully enabled CUDA support for NVIDIA GeForce RTX 4070 Laptop GPU
• ✅ Container Build System: Native DevEnv containers with dev/prod configurations
• ✅ Centralized Configuration: app_config.nix with modular DevEnv structure
• ✅ Environment Management: Dynamic dev/prod mode switching
• ✅ Documentation: Comprehensive guides and implementation reports
• ✅ Testing Infrastructure: Smoke tests, database connectivity, validation scripts
• ✅ Code Cleanup: Moved legacy scripts to backup, organized project structure

Key achievements:

• PyTorch CUDA working with GPU acceleration
• 6 comprehensive test suites with 12 individual tests
• Native container functionality without external Docker
• Centralized configuration system
• Complete documentation and guides

Fixes CUDA detection issue by removing problematic GPU visibility environment variables.

Summary by CodeRabbit

• New Features

  • Centralized app configuration and unified manage command for setup, deploy, container lifecycle, and service tasks.
  • Health endpoints added (root and /healthz).
  • Dev and Prod container images with production-ready entrypoints and DB readiness/migration handling.

• Improvements

  • Environment-first config and safer secret handling; env-driven DB configuration and clearer mode handling.
  • DevEnv restructuring with mode-aware scripts, container workflows, and LD_LIBRARY_PATH handling.

• Documentation

  • Major README overhaul and many guides (centralized config, containers, testing, deployment, CUDA diagnostics).

• Tests

  • New smoke, config, DB connectivity, container workflow and unit tests; pytest config added.

• Chores

  • .dockerignore/.gitignore updates, status summary artifact, Makefile and container layout added.