feat: build APK packages for x86_64 and aarch64

Uses a matrix strategy with Go cross-compilation (GOARCH + CARCH)
so both architectures build in the same amd64 container.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitea/workflows/apk-publish.yml

@@ -10,6 +10,14 @@ jobs:
       - ubuntu-24.04
     container:
       image: alpine:latest
+      options: --platform linux/amd64
+    strategy:
+      matrix:
+        include:
+          - goarch: amd64
+            pkgarch: x86_64
+          - goarch: arm64
+            pkgarch: aarch64
     steps:
       - name: Install build dependencies
         run: |
@@ -39,6 +47,7 @@ jobs:
           pkgname="axolotl"
 
           sed -i "s/pkgver=.*/pkgver=$pkgver/" packaging/alpine/APKBUILD
+          sed -i "s/^arch=.*/arch=\"${{ matrix.pkgarch }}\"/" packaging/alpine/APKBUILD
 
           git archive --format=tar.gz --prefix="$pkgname-$pkgver/" -o "packaging/alpine/$pkgname-$pkgver.tar.gz" HEAD
 
@@ -49,7 +58,7 @@ jobs:
         run: su build -c "cd $PWD/packaging/alpine && abuild checksum"
 
       - name: Build package
-        run: su build -c "cd $PWD/packaging/alpine && abuild -r"
+        run: su build -c "cd $PWD/packaging/alpine && GOARCH=${{ matrix.goarch }} CARCH=${{ matrix.pkgarch }} abuild -r"
 
       - name: Publish to Gitea Registry
         run: |