fix(ci): consume the published MinIO image (#7870)

Switch every CI job that starts MinIO to the public
`ghcr.io/block/buzz-minio:latest` image published by #7869. Integration
jobs pull the image; image builds stay in the separate, path-filtered
publisher workflow.

- Apply the CI Compose override to both desktop integration shards,
backend integration, relay E2E, and mesh lifecycle, including
script-mediated Compose calls. Both the server and bucket initializer
use the Buzz image.
- Override both MinIO images in Helm's quickstart CI values, covering
the server, bucket initializer, and relay's wait-for-bucket init
container in the gated kind installation.
- Select integration and mesh checks when either Compose file changes,
with regression coverage using the real pinned `dorny/paths-filter`
action.

### Publication verified

#7869 is merged, and [the first main-branch
publication](https://github.com/block/buzz/actions/runs/36021389137/job/107706874954)
succeeded. An anonymous pull using an empty Docker configuration
returned the publisher's digest:
`sha256:b8470bbeafbf57b20c86cf63804682b714bdcfdbb517f3770247e321e623f48f`.
This PR is rebased onto main and ready for consumer integration checks.

### Validation

- Ran the repository's MinIO smoke script against the actual published
AMD64 image: healthy startup, bucket initialization, object
upload/read/delete, and rejection of anonymous reads all passed. Used
the rendered CI Compose services with isolated local ports and resource
names.
- Verified `mc` runs and writes its configuration as Helm's non-root
UID/GID 65532 with dropped capabilities and no privilege escalation.
- Helm 3.16.4 lint and quickstart rendering passed; all three rendered
MinIO container references use the Buzz image.
- All 14 CI selection cases and the required-context isolation check
passed. Mesh workflow passes actionlint; shared workflows pass with
shellcheck disabled for pre-existing findings.
- Fresh repository-wide review traced workflow and script consumers and
found no remaining CI image omissions. Full application integration
checks and a real kind installation have not been run locally.

---------

Signed-off-by: Tyler Longwell <tlongwell@squareup.com>

.github/workflows/mesh-lifecycle.yml

@@ -22,6 +22,8 @@ on:
       - 'scripts/ci-mesh-lifecycle-smoke.sh'
       - 'scripts/start-relay-for-tests.sh'
       - '.github/workflows/mesh-lifecycle.yml'
+      - 'docker-compose.yml'
+      - 'docker-compose.ci.yml'
   pull_request:
     paths:
       - 'crates/buzz-mesh-smoke/**'
@@ -34,6 +36,8 @@ on:
       - 'scripts/ci-mesh-lifecycle-smoke.sh'
       - 'scripts/start-relay-for-tests.sh'
       - '.github/workflows/mesh-lifecycle.yml'
+      - 'docker-compose.yml'
+      - 'docker-compose.ci.yml'
   workflow_dispatch:
 
 concurrency:
@@ -45,6 +49,8 @@ env:
 
 jobs:
   lifecycle-smoke:
+    env:
+      COMPOSE_FILE: docker-compose.yml:docker-compose.ci.yml
     name: Relay-Driven Mesh Lifecycle Smoke
     runs-on: ubuntu-24.04
     timeout-minutes: 45