fix(flake): apply claude-code overlay to all platforms

The custom claude-code overlay (for GCS-based builds) was only being
applied to darwinModules. Extract to shared customUnstableOverlays and
apply to nixosModules and nixosModulesUnstable as well.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

flake.nix

@@ -89,11 +89,20 @@
     };
 
 
+    # Shared unstable overlays for custom package builds
+    customUnstableOverlays = [
+      # Override claude-code in unstable to use our custom GCS-based build
+      # (needed for corporate networks that block npm registry)
+      (ufinal: uprev: {
+        claude-code = uprev.callPackage ./packages/claude-code {};
+      })
+    ];
+
     nixosModules = [
       ./roles
       inputs.home-manager.nixosModules.home-manager
       {
-        nixpkgs.overlays = [ (mkBaseOverlay {}) ];
+        nixpkgs.overlays = [ (mkBaseOverlay { unstableOverlays = customUnstableOverlays; }) ];
       }
       (mkHomeManagerConfig {
         sharedModules = [ inputs.plasma-manager.homeModules.plasma-manager ];
@@ -106,7 +115,7 @@
       inputs.home-manager-unstable.nixosModules.home-manager
       inputs.jovian.nixosModules.jovian
       {
-        nixpkgs.overlays = [ (mkBaseOverlay {}) ];
+        nixpkgs.overlays = [ (mkBaseOverlay { unstableOverlays = customUnstableOverlays; }) ];
       }
       (mkHomeManagerConfig {
         sharedModules = [ inputs.plasma-manager-unstable.homeModules.plasma-manager ];
@@ -117,17 +126,7 @@
       ./roles/darwin.nix
       inputs.home-manager.darwinModules.home-manager
       {
-        nixpkgs.overlays = [
+        nixpkgs.overlays = [ (mkBaseOverlay { unstableOverlays = customUnstableOverlays; }) ];
-          (mkBaseOverlay {
-            # Override claude-code in unstable to use our custom GCS-based build
-            # (needed for corporate networks that block npm registry)
-            unstableOverlays = [
-              (ufinal: uprev: {
-                claude-code = uprev.callPackage ./packages/claude-code {};
-              })
-            ];
-          })
-        ];
       }
       (mkHomeManagerConfig { sharedModules = []; })
     ];