.github,docker: add cuda13 architecture support (#551)

Add `cuda13` as a supported build architecture, targeting the
`ghcr.io/ggml-org/llama.cpp:server-cuda13` upstream base image.

The `server-cuda13` image ships with CUDA 13 libraries, providing
improved performance on recent NVIDIA hardware compared to the existing
`server-cuda` (CUDA 12) image. Users with newer GPUs (e.g., RTX
50-series) benefit from reduced model load latency and higher token
throughput.

- Add `cuda13` to the allowed architectures list in
`docker/build-container.sh`
- Add `cuda13` to the CI matrix in `.github/workflows/containers.yml` so
the container is built and pushed automatically

.github/workflows/containers.yml

@@ -29,7 +29,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        platform: [intel, cuda, vulkan, cpu, musa, rocm]
+        platform: [intel, cuda, cuda13, vulkan, cpu, musa, rocm]
       fail-fast: false
     steps:
       - name: Checkout code

docker/build-container.sh

@@ -27,7 +27,7 @@ ARCH=$1
 PUSH_IMAGES=${2:-false}
 
 # List of allowed architectures
-ALLOWED_ARCHS=("intel" "vulkan" "musa" "cuda" "cpu" "rocm")
+ALLOWED_ARCHS=("intel" "vulkan" "musa" "cuda" "cuda13" "cpu" "rocm")
 
 # Check if ARCH is in the allowed list
 if [[ ! " ${ALLOWED_ARCHS[@]} " =~ " ${ARCH} " ]]; then