Remove Nixpacks configuration files for backend and frontend; update Coolify deployment guide to reflect changes in directory structure and configuration requirements.

Co-authored-by: Copilot <copilot@github.com>

backend/nixpacks.toml

@@ -1,13 +0,0 @@
-# Nixpacks configuration for the FastAPI backend
-
-[phases.setup]
-nixpkgsArchive = "88a9d1386465831607986442fd9c8c0e7a1b2f5"
-aptPkgs = ["git"]
-
-[phases.install]
-# Nixpacks auto-detects Python and runs pip install -r requirements.txt
-
-[build]
-
-[deploy]
-startCommand = "uvicorn backend.app.main:app --host 0.0.0.0 --port 8000"