[Task] — Integrated-test & examples Dockerfiles run as root, no HEALTHCHECK, no LABEL

- severity: Medium; files: all of `shenyu-integrated-test/*/Dockerfile` and `shenyu-examples/*/Dockerfile` (verified via grep — zero `USER`/`HEALTHCHECK`/`LABEL` matches)
- description: e.g. `shenyu-integrated-test-http/Dockerfile` ends with `CMD java -jar ${APP_NAME}.jar` with no `USER`, `HEALTHCHECK`, or OCI `LABEL`. The release dist Dockerfiles (`shenyu-dist/shenyu-{admin,bootstrap}-dist/docker/Dockerfile`) correctly set `USER shenyu`, but these do not.
- impact: Containers run as root; no liveness probe; no image metadata.
- suggested_fix: Add a non-root `USER`, `HEALTHCHECK`, and `LABEL org.opencontainers.image.*`.
- confidence: High

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_Identified during the 2026-08-02 deep re-scan; full list in [`docs/scan2-2026-08-02/06-medium-tiers.md`](docs/scan2-2026-08-02/06-medium-tiers.md)._

Review all Dockerfiles under shenyu-integrated-test/* and shenyu-examples/*, using shenyu-dist/shenyu-{admin,bootstrap}-dist/docker/Dockerfile as the existing reference. Confirm the required non-root USER, HEALTHCHECK, and OCI image LABEL values before editing. Done means every listed Dockerfile contains all three directives and the grep scan no longer reports missing matches.

Written by the indexing model from the issue text.