ci: digest-pin runner-image v0.1.0 (was :v2)

Drops the ad-hoc :vN tag scheme — see runner-image#semver. Consumers
now reference tag + digest so the resolved image is byte-identical
across runs.

.gitea/workflows/ci.yml

@@ -12,7 +12,7 @@ jobs:
     # Bespoke runner image (Ubuntu 24.04 + make + git + node + go via
     # actions/setup-go). See git.librete.ch/public/runner-image.
     container:
-      image: git.librete.ch/public/runner-image:v2
+      image: git.librete.ch/public/runner-image:v0.1.0:9d1e204fe8e06b7d16cdc8da0c7077fa4171daef62099cc8c09993834e576ca5
     timeout-minutes: 5
     steps:
       - name: Checkout

.gitea/workflows/deploy.yml

@@ -34,7 +34,7 @@ jobs:
     # + perl + ssh, runner user pre-joined to docker gid 998 so the
     # auto-mounted /var/run/docker.sock is writable without --user root.
     container:
-      image: git.librete.ch/public/runner-image:v2
+      image: git.librete.ch/public/runner-image:v0.1.0:9d1e204fe8e06b7d16cdc8da0c7077fa4171daef62099cc8c09993834e576ca5
     timeout-minutes: 20
     if: ${{ vars.DEPLOY_ENABLED == 'true' }}
     steps: