feat: replace local opencode with upstream flake input v1.1.27

- Add `opencode` flake input pinned to v1.1.27 for stability
- Remove local `pkgs/opencode` derivation and overlay
- Add `opencode` and `opencode-desktop` to `pkgs/default.nix` from input

flake.nix

@@ -3,6 +3,7 @@
 
   inputs = {
     nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    opencode.url = "github:anomalyco/opencode/v1.1.27";
 
     # Optional: Add stable channel if needed
     # nixpkgs-stable.url = "github:NixOS/nixpkgs/nixos-24.05";
@@ -36,18 +37,18 @@
       system: let
         pkgs = pkgsFor system;
       in
-        import ./pkgs {inherit pkgs;}
+        import ./pkgs {inherit pkgs inputs;}
     );
 
     # Overlays - can be imported in your system configuration
     overlays = {
       # Default overlay: adds all custom packages
       default = final: prev:
-        import ./pkgs {pkgs = final;};
+        import ./pkgs {pkgs = final; inputs = inputs;};
 
       # Individual overlays for more granular control
       additions = final: prev:
-        import ./pkgs {pkgs = final;};
+        import ./pkgs {pkgs = final; inputs = inputs;};
 
       modifications = final: prev:
         import ./overlays/mods {inherit prev;};