Keep install.sh diagnostics in parity with the install.ps1 xpu family

install.ps1 now classifies an /xpu index leaf as family xpu / branch xpu, so
mirror the same two cases in _tauri_torch_index_family and _tauri_gpu_branch.
These feed the [TAURI:DIAG] line only, and a Linux user can already reach the
xpu index via UNSLOTH_TORCH_INDEX_FAMILY, where it previously reported
auto/unknown. Linux Intel auto-detection is not added here.

Author: danielhanchen

install.sh

@@ -487,6 +487,7 @@ _tauri_torch_index_family() {
         */cu128) echo "cu128" ;;
         */cu130) echo "cu130" ;;
         */cpu) echo "cpu" ;;
+        */xpu) echo "xpu" ;;
         */rocm[0-9]*.[0-9]*)
             _diag_family=${_diag_url##*/}
             case "$_diag_family" in
@@ -522,6 +523,7 @@ _tauri_gpu_branch() {
                 echo "rocm"
             fi ;;
         radeon) echo "rocm_radeon" ;;
+        xpu) echo "xpu" ;;
         cpu) echo "cpu" ;;
         none) echo "no_torch" ;;
         *) echo "unknown" ;;