feat(local-inference): replace ollama with llama-swap + llama.cpp on zix790prors

- Add local-inference NixOS role using llama-swap (from nixpkgs-unstable)
  with llama.cpp (CUDA-enabled, from nixpkgs-unstable)
- Serves Qwen3.6-35B-A3B via HuggingFace auto-download with --cpu-moe
- Add nixosSpecialArgs for nixpkgs-unstable module access
- Configure opencode with llama-local provider pointing to zix790prors:8080
- Update gptel from Ollama backend to OpenAI-compatible llama-swap backend
- Remove ollama service from zix790prors

flake.nix

@@ -104,6 +104,11 @@
           };
         };
 
+      # Common specialArgs passed to all NixOS systems
+      nixosSpecialArgs = {
+        inherit nixpkgs-unstable;
+      };
+
       # Shared unstable overlays for custom package builds
       customUnstableOverlays = [
         # Override claude-code in unstable to use our custom GCS-based build
@@ -149,6 +154,7 @@
     in
     {
       nixosConfigurations.nix-book = nixpkgs.lib.nixosSystem rec {
+        specialArgs = nixosSpecialArgs;
         system = "x86_64-linux";
         modules = nixosModules ++ [
           ./machines/nix-book/configuration.nix
@@ -166,6 +172,7 @@
       };
 
       nixosConfigurations.boxy = nixpkgs.lib.nixosSystem rec {
+        specialArgs = nixosSpecialArgs;
         system = "x86_64-linux";
         modules = nixosModules ++ [
           ./machines/boxy/configuration.nix
@@ -179,6 +186,7 @@
       };
 
       nixosConfigurations.gym-box = nixpkgs.lib.nixosSystem rec {
+        specialArgs = nixosSpecialArgs;
         system = "x86_64-linux";
         modules = nixosModules ++ [
           ./machines/gym-box/configuration.nix
@@ -191,6 +199,7 @@
       };
 
       nixosConfigurations.zix790prors = nixpkgs.lib.nixosSystem rec {
+        specialArgs = nixosSpecialArgs;
         system = "x86_64-linux";
         modules = nixosModules ++ [
           ./machines/zix790prors/configuration.nix
@@ -212,6 +221,7 @@
 
       # Live USB ISO configuration
       nixosConfigurations.live-usb = nixpkgs.lib.nixosSystem rec {
+        specialArgs = nixosSpecialArgs;
         system = "x86_64-linux";
         modules = nixosModules ++ [
           ./machines/live-usb/configuration.nix
@@ -236,6 +246,7 @@
 
       # ZFS/NFS server configuration
       nixosConfigurations.john-endesktop = nixpkgs.lib.nixosSystem rec {
+        specialArgs = nixosSpecialArgs;
         system = "x86_64-linux";
         modules = nixosModules ++ [
           ./machines/john-endesktop/configuration.nix