ci(prerelease): add ampere flavour alongside ada and blackwell

Adds ampere (CUDA compute capability sm_86) to both the build-neuron
and package-neuron matrices, so helexa-neuron-ampere RPMs are built
and published alongside helexa-neuron-ada and helexa-neuron-blackwell.

The prerelease spec already lists ampere in its Conflicts: clause, so
no spec change is needed.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitea/workflows/build-prerelease.yml

@@ -94,6 +94,13 @@ jobs:
       fail-fast: false
       matrix:
         include:
+          - flavour: ampere
+            compute_cap: "86"
+            runner: cuda-13.0
+            cuda_home: /usr/local/cuda-13.0
+            build_jobs: 8
+            nvcc_threads: 4
+            cargo_features: "cuda cudnn flash-attn"
           - flavour: ada
             compute_cap: "89"
             runner: cuda-13.0
@@ -193,6 +200,7 @@ jobs:
       fail-fast: false
       matrix:
         include:
+          - flavour: ampere
           - flavour: ada
           - flavour: blackwell
     steps: