fix(ci): add rustup install/update step to build job

The gitea runner user on beast doesn't have Rust installed.
Reuses existing installation on subsequent runs.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitea/workflows/build-release.yml

@@ -23,6 +23,15 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
+      - name: Install/update Rust toolchain
+        run: |
+          if command -v rustup &> /dev/null; then
+            rustup update stable
+          else
+            curl --proto '=https' --tlsv1.2 --silent --show-error --fail https://sh.rustup.rs | sh -s -- -y
+          fi
+          echo "${HOME}/.cargo/bin" >> "$GITHUB_PATH"
+
       - name: Clone mistral.rs at tag
         run: |
           git clone --depth 1 --branch "${{ inputs.tag }}" \