Implement hybrid package management: stable + selective unstable

- Add nixpkgs-unstable input to flake.nix
- Configure specialArgs to pass pkgs-unstable to all system configs
- Update desktop/dev.nix to use windsurf from unstable packages
- Create comprehensive documentation in README-hybrid-packages.md
- Enable selective use of cutting-edge packages while maintaining system stability

Usage: Add pkgs-unstable parameter to any .nix file and use pkgs-unstable.package-name
Example: pkgs-unstable.windsurf for latest Windsurf editor

README-hybrid-packages.md

@@ -0,0 +1,117 @@
+# Hybrid Package Management: Stable + Unstable
+
+This NixOS configuration uses a hybrid approach where the system runs on the stable NixOS 24.05 branch but can selectively use packages from the unstable branch when needed.
+
+## How It Works
+
+The `flake.nix` includes both stable and unstable nixpkgs inputs:
+
+```nix
+inputs = {
+  nixpkgs.url = "nixpkgs/nixos-24.05";           # Stable base
+  nixpkgs-unstable.url = "nixpkgs/nixos-unstable"; # Unstable packages
+  # ... other inputs
+};
+```
+
+The unstable packages are made available to all system configurations via `specialArgs`:
+
+```nix
+nixosConfigurations = {
+  framework = nixpkgs.lib.nixosSystem {
+    system = "x86_64-linux";
+    specialArgs = {
+      pkgs-unstable = import nixpkgs-unstable {
+        system = "x86_64-linux";
+        config.allowUnfree = true;
+      };
+    };
+    modules = [ /* ... */ ];
+  };
+};
+```
+
+## Using Unstable Packages
+
+### In System Configuration Files
+
+To use an unstable package in any `.nix` configuration file:
+
+1. **Add `pkgs-unstable` to the function parameters:**
+   ```nix
+   { config, pkgs, pkgs-unstable, ... }:
+   ```
+
+2. **Use the unstable package:**
+   ```nix
+   environment.systemPackages = with pkgs; [
+     # Stable packages
+     firefox
+     git
+     
+     # Unstable packages
+     pkgs-unstable.windsurf
+     pkgs-unstable.some-other-package
+   ];
+   ```
+
+### Example: Current Usage
+
+See `desktop/dev.nix` for a working example:
+
+```nix
+{ config, pkgs, pkgs-unstable, ... }:
+
+{
+  environment.systemPackages = with pkgs; [
+    # Stable packages
+    nodejs
+    rpi-imager
+    
+    # Unstable packages
+    pkgs-unstable.windsurf  # Use windsurf from unstable
+  ];
+}
+```
+
+## When to Use Unstable Packages
+
+Use unstable packages when:
+- A package is not available in the stable branch
+- You need a newer version with specific features or bug fixes
+- You're developing with cutting-edge tools
+
+## Benefits of This Approach
+
+1. **System Stability**: Core system components use stable, well-tested packages
+2. **Package Availability**: Access to the latest packages when needed
+3. **Selective Updates**: Choose which packages to get from unstable
+4. **Easy Maintenance**: Clear separation between stable and unstable dependencies
+
+## Adding New Unstable Packages
+
+To add a new unstable package:
+
+1. Find the configuration file where you want to add the package
+2. Ensure the file accepts `pkgs-unstable` parameter
+3. Add `pkgs-unstable.package-name` to the appropriate list
+4. Test with `nixos-rebuild dry-run --flake .#framework`
+5. Apply with `nixos-rebuild switch --flake .#framework`
+
+## Updating Packages
+
+- **Stable packages**: Updated when you update the flake lock
+- **Unstable packages**: Updated when you run `nix flake update`
+
+To update only unstable packages:
+```bash
+nix flake lock --update-input nixpkgs-unstable
+```
+
+## Current Unstable Packages in Use
+
+- `windsurf` - Modern code editor (in `desktop/dev.nix`)
+
+---
+
+This hybrid approach gives you the stability of NixOS stable with the flexibility to use cutting-edge packages when needed.