fix(ci): install python3 via apk — act job container is alpine, not debian

Run 467 log (job 1985): 'python3 missing — installing on alpine' then
'apt-get: command not found' → exit 127. The act_runner container is
node:20-alpine-ish; the provisioning step now detects apk first, apt
second, and fails loudly with a diagnostic if neither exists.

.gitea/workflows/ci.yml

@@ -15,17 +15,25 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - name: Ensure python3 available (runner image may lack it)
+      - name: Ensure python3 + PyYAML (act container is alpine-based, no python preinstalled)
         run: |
+          . /etc/os-release
+          echo "job OS: $ID"
           if command -v python3 >/dev/null 2>&1; then
             python3 --version
-          else
-            . /etc/os-release
-            echo "python3 missing — installing on $ID $VERSION_CODENAME"
+          elif command -v apk >/dev/null 2>&1; then
+            echo "installing via apk"
+            apk add --no-cache python3 py3-yaml
+            python3 --version
+            python3 -c "import yaml" || { echo "yaml import failed after py3-yaml; trying pip"; python3 -m pip install --break-system-packages pyyaml; }
+          elif command -v apt-get >/dev/null 2>&1; then
+            echo "installing via apt"
             apt-get update -qq
             apt-get install -y -qq python3 python3-yaml
             python3 --version
-            python3 -c "import yaml" && echo "PyYAML OK"
+          else
+            echo "no python3 and no apk/apt in job image — cannot run CI checks"
+            exit 1
           fi
       - run: node --version