Feat: TEM-11 container hardening

[Chmokachka]

Summary

Container hardening for the official templates (TEM-11). Three self-contained improvements:

1. tini as PID 1 + signal forwarding — install tini in base/Dockerfile and set ENTRYPOINT ["/usr/bin/tini", "-g", "--"] (keeping CMD ["/start.sh"]). Previously start.sh (bash) ran as PID 1, so it ignored SIGTERM and never reaped zombies — docker stop/pod stop waited out the grace period and got SIGKILLed. tini forwards signals to the process group (-g) for prompt, graceful shutdown and reaps orphans. It also gives every family a deterministic PID 1, superseding the inherited NVIDIA CUDA entrypoint (so the autoresearch ENTRYPOINT override could be dropped — it now inherits tini from base).

2. OCI image labels — a shared _oci-labels bake target in shared/versions.hcl that every family's *-base inherits, plus per-family title/description. Adds provenance/metadata: source, url, documentation, vendor, version, revision (github.sha), created (CI build timestamp via a new docker-setup build-date output). revision/created are wired through the bake step env in all build workflows.

3. Pin autoresearch source to an immutable commit SHA — AUTORESEARCH_REF default master → d173f4ec6353213bf644631a8d30fa80974cc65f (current master tip, so no behavior change). Since git clone --branch can't take a SHA, the clone is now git init + shallow fetch <sha> + checkout --detach for reproducible builds. Still overridable via ARG; bump the SHA to update.