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

flake.nix

@@ -3,6 +3,7 @@
 
   inputs = {
     nixpkgs.url = "nixpkgs/nixos-24.05";
+    nixpkgs-unstable.url = "nixpkgs/nixos-unstable";
     nixos-hardware.url = "github:NixOS/nixos-hardware/master";
     home-manager = {
       url = "github:nix-community/home-manager/release-24.05";
@@ -15,10 +16,16 @@
     };
   };
 
-  outputs = { self, nixpkgs, nixos-hardware, home-manager, plasma-manager }: {
+  outputs = { self, nixpkgs, nixpkgs-unstable, nixos-hardware, home-manager, plasma-manager }: {
     nixosConfigurations = {
       framework =  nixpkgs.lib.nixosSystem {
         system = "x86_64-linux";
+        specialArgs = {
+          pkgs-unstable = import nixpkgs-unstable {
+            system = "x86_64-linux";
+            config.allowUnfree = true;
+          };
+        };
         modules = [
           home-manager.nixosModules.home-manager
           nixos-hardware.nixosModules.framework-16-7040-amd
@@ -36,6 +43,12 @@
       };
       aurora = nixpkgs.lib.nixosSystem {
         system = "x86_64-linux";
+        specialArgs = {
+          pkgs-unstable = import nixpkgs-unstable {
+            system = "x86_64-linux";
+            config.allowUnfree = true;
+          };
+        };
         modules = [
           home-manager.nixosModules.home-manager
           ./systems/common.nix