chore(packages/llama-cpp): bump to b8815 and add spirv-headers dependency

packages/llama-cpp/default.nix

@@ -7,12 +7,12 @@
   vulkanSupport = true;
 }).overrideAttrs
   (oldAttrs: rec {
-    version = "8680";
+    version = "8815";
     src = pkgs.fetchFromGitHub {
       owner = "ggml-org";
       repo = "llama.cpp";
       tag = "b${version}";
-      hash = "sha256-tJCA19BQs0vZc0VjPnbIrh3CJFxyPL6Ne4oIG4gfozw=";
+      hash = "sha256-QJsGBHLdvFfMXZJSk9D76b7v6DP06NaTYztHv41o/CA=";
       leaveDotGit = true;
       postFetch = ''
         git -C "$out" rev-parse --short HEAD > $out/COMMIT
@@ -20,6 +20,11 @@
       '';
     };
 
+    # Add SPIR-V Headers for Vulkan Backend
+    # Newer llama.cpp requires spirv/unified1/spirv.hpp which isn't
+    # pulled in by vulkan-headers alone.
+    buildInputs = (oldAttrs.buildInputs or [ ]) ++ [ pkgs.spirv-headers ];
+
     # Auto CPU Optimizations
     cmakeFlags = (oldAttrs.cmakeFlags or [ ]) ++ [
       "-DGGML_CUDA_ENABLE_UNIFIED_MEMORY=1"