feat: add NixOS support, Go, and Ruby on Rails; remove Rust

- Add nixos/ directory with declarative flake.nix and home.nix for NixOS
- Make all setup scripts NixOS-aware with proper detection and early exit
- Update bashrc, zshrc, and aliases with Go, Ruby on Rails, and Nix profile paths
- Replace Rust/Cargo references in shell configs with rbenv/Ruby on Rails
- Update README with NixOS quick start and full documentation

scripts/01-package-install.sh

@@ -3,6 +3,7 @@
 # 01-package-install.sh
 # Installs system packages and Flatpak applications.
 # Relies on DISTRO and PACKAGE_MANAGER being set by the caller.
+# Supports NixOS (nix profile), Fedora (dnf), and Debian/Ubuntu (apt).
 
 echo "--- Starting Package Installation ---"
 
@@ -11,6 +12,26 @@ if [ -z "$DISTRO" ] || [ -z "$PACKAGE_MANAGER" ]; then
     exit 1
 fi
 
+# ── NixOS path ─────────────────────────────────────────────
+if [ "$DISTRO" == "nixos" ]; then
+    echo "NixOS detected: packages are managed declaratively via nixos/flake.nix"
+    echo "and nixos/home.nix. Run the main-setup.sh workflow or apply manually."
+    echo ""
+    echo "  sudo nixos-rebuild switch --flake ~/dotfiles/nixos#nixos"
+    echo "  home-manager switch --flake ~/dotfiles/nixos#blake"
+    echo ""
+    echo "If you want imperative ad-hoc packages, uncomment the lines below"
+    echo "or run manually:"
+    echo ""
+    echo "  nix profile install nixpkgs#<package>"
+    echo ""
+    echo "Skipping imperative package installation."
+    echo "--- Package Installation Finished ---"
+    exit 0
+fi
+
+# ── Traditional distro path (Fedora / Ubuntu / Debian) ─────
+
 # Define base package list
 BASE_PACKAGE_LIST=(
     ansible
@@ -127,7 +148,7 @@ done
 if [ "$PACKAGE_MANAGER" == "apt" ] && command -v fdfind &>/dev/null && ! command -v fd &>/dev/null; then
     if dpkg-query -W -f='${Status}' "fd-find" 2>/dev/null | grep -q "ok installed"; then
         echo "Creating symlink for fd from fdfind..."
-        sudo ln -sf /usr/bin/fdfind /usr/local/bin/fd 
+        sudo ln -sf /usr/bin/fdfind /usr/local/bin/fd
     fi
 fi