ci: bound CI storage; don't bridge image-build jobs

- deploy/runner/prune.sh + windygit-ci-prune.timer (6h): age-based prune
  of the CI-only dind (containers, finished-job volumes, images/builder
  cache >7d) plus a hard 60 GB cap. Only that daemon, over its own TCP
  socket; never the host's Docker. It was 38 GB and unbounded — the same
  class of growth that filled Kit 0 on 09-01.
- pr_status_bridge: jobs named *docker* are not posted. Job containers
  have no daemon by design (I-5), so they are red on every commit; a
  permanent red X teaches everyone to ignore red.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

deploy/runner/prune.sh

@@ -0,0 +1,28 @@
+#!/usr/bin/env bash
+# Keep CI storage bounded (2026-09-23).
+#
+# Kit 0's 09-01 wipe began with CI `_work` dirs (74 GB) + Docker filling the
+# disk. Windy Git's runners have no host `_work` dir — every job runs in a
+# container inside the CI-only dind — so the thing that grows here is dind's
+# image/volume store (38 GB when this was written, never pruned). This prunes
+# ONLY that daemon, over its own socket. It never touches the host's Docker.
+#
+# In-use images/volumes are never removed, so a running job is safe.
+set -euo pipefail
+CAP_GB="${CI_STORAGE_CAP_GB:-60}"
+D=(docker exec windy-git-runner-dind-1 docker)
+
+"${D[@]}" container prune -f --filter until=6h >/dev/null
+"${D[@]}" volume prune -af >/dev/null            # job workspaces of finished jobs
+"${D[@]}" image prune -af --filter until=168h >/dev/null
+"${D[@]}" builder prune -af --filter until=168h >/dev/null 2>&1 || true
+
+used_gb=$(du -s --block-size=1G /var/lib/docker/volumes/windy-git-runner_dind-storage | cut -f1)
+if (( used_gb > CAP_GB )); then
+  # Over the cap even after the age-based pass: drop every unused image. The
+  # next jobs re-pull (the act image is ~2 GB) — slower, never wrong.
+  "${D[@]}" image prune -af >/dev/null
+  used_gb=$(du -s --block-size=1G /var/lib/docker/volumes/windy-git-runner_dind-storage | cut -f1)
+fi
+echo "ci storage ${used_gb}G (cap ${CAP_GB}G)"
+(( used_gb <= CAP_GB )) || { echo "STILL OVER CAP"; exit 1; }