chore(blender): pin nixpkgs-blender and drop obsolete OIDN override

nixpkgs-blender tracked the nixpkgs master branch, so every `just up` re-bumped it and started a full Blender/CUDA source rebuild even though Blender stayed at 5.2.2 LTS. Pin it to a fixed rev so bumps are deliberate.

The OIDN cmake override is obsolete: nixpkgs#545542 made setupCudaHook add nvcc to CUDAToolkit_ROOT, fixing the CMake 4.3+ split-root failure (nixpkgs#544701). Dropping it also stops Blender's derivation from depending on nixpkgs-stable.

flake.lock

@@ -627,8 +627,8 @@
       },
       "original": {
         "owner": "nixos",
-        "ref": "master",
         "repo": "nixpkgs",
+        "rev": "4b8338e3113dc41bcf7695f56dc372107b7ff4c9",
         "type": "github"
       }
     },

flake.nix

@@ -108,8 +108,10 @@
       inputs.nixpkgs.follows = "nixpkgs";
     };
 
-    # Track Blender from master while keeping its lock entry independent from regular nixpkgs.
-    nixpkgs-blender.url = "github:nixos/nixpkgs/master";
+    # Pinned nixpkgs for Blender (5.2 LTS + CUDA/OptiX).  Keeping it on a fixed
+    # rev stops `just up` from re-bumping this input and triggering a full
+    # Blender/CUDA source rebuild; bump the rev deliberately when needed.
+    nixpkgs-blender.url = "github:nixos/nixpkgs/4b8338e3113dc41bcf7695f56dc372107b7ff4c9";
 
     nixos-apple-silicon = {
       url = "github:nix-community/nixos-apple-silicon";

outputs/default.nix

@@ -53,13 +53,6 @@ let
           # for unrelated GPU architectures.
           cudaCapabilities = [ "8.9" ];
         };
-        overlays = lib.optional (system == "x86_64-linux") (
-          _: prev: {
-            # CMake 4.2+ breaks OIDN's nested CUDA build with nixpkgs' split CUDAToolkit_ROOT.
-            # https://github.com/NixOS/nixpkgs/issues/544701
-            openimagedenoise = prev.openimagedenoise.override { cmake = pkgs-stable.cmake; };
-          }
-        );
       };
 
       pkgs-x64 = import nixpkgs {