fix(ci): nothing a CI job starts outlives it, even when the runner kills the job

A migration-smoke stack (PostgreSQL and SeaweedFS) ran on the shared
runner for two days. Every CI script removes its stack in an EXIT trap,
but a trap never runs when the runner kills the job container: a
cancelled job, or the runner's own time limit (Gitea 1.24 ignores
timeout-minutes). Reproduced: SIGKILL of the infrastructure smoke
mid-run leaves exactly that stack running.

Cleanup now has three layers:
- the script's own trap, unchanged;
- a final `if: always()` step in every job that starts stacks
  (infrastructure-smoke, migration-smoke, image-build, deploy-smoke)
  runs `scripts/ci-sweep.sh --job`, which removes everything that job
  started at any age;
- a first step in each of those jobs runs `scripts/ci-sweep.sh --stale`,
  which removes CI stacks older than three hours: what a killed job left
  before it could clean up.

How stacks are found is defined once, in scripts/lib/ci-project.sh:
- every CI Compose project is named `ekklesia-ci-<run>-<attempt>-<job
  key>-<kind>-<unique>`, and Compose labels its containers, networks and
  volumes with that name;
- the deploy smoke labels everything it starts outside Compose:
  browser, kiosk and driver containers, the kiosk volume, built images;
- images also record when CI built them. An image's own creation time
  can be its base's (BuildKit, metadata-only builds), and the sweep
  removed a brand-new image as "old" until it stopped trusting that.

The job key is per matrix leg, so one topology's cleanup cannot remove
the other's running stack. The sweep never touches anything outside the
ekklesia-ci- prefix, disconnects rather than removes a job container
attached to a stack's network, and refuses --job outside CI. Network
creation times are read as RFC 3339; Docker's default form was
unparseable.

scripts/test-ci-sweep.sh proves all of that against real Docker, and
CI runs it before relying on it. security.md and testing.md document
the rule, and that it complements, not replaces, a runner-side reaper.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

docs/development/security.md

@@ -746,6 +746,33 @@ The declarations are kept deliberately: they are already correct for a supported
 for GitHub Actions, and keeping them means the upgrade does not require re-deriving the intent. They
 are documented as ignored, not removed.
 
+### Disposable stacks never outlive their job
+
+Every CI script removes its own Compose stack in an `EXIT` trap, but a trap never runs when the runner
+kills the job container: a cancelled job, or the runner's own time limit. One such stack ran on the
+shared runner for two days. So stack cleanup has three layers:
+
+- **The script's own trap**, for every ordinary failure.
+- **A final `if: always()` step** in every job that starts stacks: `scripts/ci-sweep.sh --job` removes
+  everything that job started, at any age, even after a failed step.
+- **A sweep before every such job starts**: `scripts/ci-sweep.sh --stale` removes anything a CI job
+  left more than three hours ago, which catches whatever a killed job could not clean up itself.
+
+A stack is found by name and label, never by guesswork (`scripts/lib/ci-project.sh`):
+
+- every CI Compose project is named `ekklesia-ci-<run>-<attempt>-<job key>-…`, and Compose labels
+  its containers, networks, and volumes with that name;
+- anything a script starts outside Compose carries `org.riverofglorymn.ekklesia.ci.project`;
+- images also carry the time CI built them, because an image's own creation time can be its base's.
+
+The job key is per matrix leg, so one leg's cleanup cannot match another's running stack. Nothing
+outside the `ekklesia-ci-` prefix is ever removed. A job container attached to a stack's network is
+disconnected, never removed.
+
+**This is not a substitute for a runner-side reaper.** A stack killed with its job is removed only
+when another job that sweeps runs on the same runner. Bounded execution and teardown are still the
+runner host's to enforce, as above.
+
 ### Runner topology is not verified
 
 **The runner topology is not verified in this repository and is not documented here as though it