* fix(renovate): pin PHP base images to digest-only updates
* feat(php85): add PHP 8.5 with Imagick and Composer
* ci: add php85 to build and PR matrices
* docs: update supported PHP version range to 8.5
* ci: enable GHA build cache for Docker image builds
* fix: address CR feedback — fix DOCKERFILE_PATH, renovate match, composer verify, drop python3-dev
* ci: use native arm64 runners for arm64 Docker builds
* ci: use build-by-digest with manifest merge for multi-arch images
Switch from direct per-arch push to a two-phase workflow:
1. Build phase pushes images by digest and uploads artifacts
2. Merge phase creates multi-arch manifest lists per PHP version
This ensures proper multi-arch manifest tags instead of
last-writer-wins race conditions between arch builds.
* fix: remove continue-on-error and suppress SC2046 shellcheck warning
Remove continue-on-error from build job so failed arch builds correctly
block the merge job from pushing incomplete manifests. Add shellcheck
disable directive for intentional word-splitting in manifest creation.
