feat(./shell.nix; ./dependencies.txt): Added env files

dependencies.txt

@@ -0,0 +1,5 @@
+flask==3.1.2
+python-dotenv
+psycopg-binary==3.2.10
+loguru
+pydantic

shell.nix

@@ -0,0 +1,19 @@
+{ pkgs ? import <nixpkgs> {} }:
+
+pkgs.mkShell {
+  buildInputs = with pkgs; [
+    python3
+  ];
+
+  shellHook = ''
+    if [ ! -d ".venv" ]; then
+      python -m venv .venv
+    fi
+
+    source .venv/bin/activate
+
+    if [ -f "dependencies.txt" ]; then
+      pip install -r dependencies.txt
+    fi
+  '';
+}