harden(cerro-torre): replace flaky cgr.dev runtime base with glibc-matched ubuntu:24.04

[hyperpolymath]

Summary

Hardens cerro-torre's container runtime stage by removing the
dependency on cgr.dev/chainguard/wolfi-base:latest, which made the
non-blocking container-stack-smoke canary flaky:

• the Chainguard free tier is unpinnable (:latest only — no version
  tags, digests rotate out), and
• it frequently returns 403 from restricted networks (reproduced
  here), so the runtime stage could not be pulled at all.

Change

Runtime base → ubuntu:24.04 (the same base, and glibc 2.39, as the
ada-builder stage). This is the only safe target:

• ct (GNAT) and cerro-sign (Rust) are dynamically linked against the
  builder's glibc. A musl base (alpine / wolfi-static) cannot run
  them; an older-glibc base (debian:stable-slim = glibc 2.36) breaks
  on the GLIBC_2.3x symbols GNAT 15 emits. Matching the builder's libc
  is required for the artefacts to run.
• ubuntu:24.04 is already pulled for the builder stage, so no additional
  base image is fetched.
• libcurl runtime + TLS roots now come from apt (libcurl4,
  ca-certificates); the non-root cerro user is created with Debian
  groupadd/useradd syntax.

Trade-off: the runtime image is larger than wolfi-base (~139 MB), accepted
in exchange for a reliably-pullable, libc-correct, pinnable-by-policy base
and a green smoke canary.

Verification (local, real containers)

Built the full multi-stage image (ada-builder + hardened runtime). The
sh.rustup.rs 403 in this sandbox blocks the Rust cerro-sign build, so
cerro-sign was stubbed for the local check only (the runtime-base
change is what's under test; the cerro-sign COPY is unchanged and
CI-exercised). Results:

• ada-builder: alr -n build → Success: Build finished successfully
• full build exports successfully; cgr.dev no longer referenced
• docker run cerro-torre:rt --version → Cerro Torre 0.1.0-alpha
• runtime user: uid=999(cerro) gid=999(cerro) (non-root preserved)
• the glibc-linked ct resolves and runs in the ubuntu:24.04 runtime

Test plan

• container-stack-smoke builds cerro-torre/Containerfile with
  docker + podman (no cgr.dev fetch; sh.rustup.rs reachable on
  GitHub runners so cerro-sign builds for real)
• resulting image runs ct --version as non-root

https://claude.ai/code/session_01744NnsooPgw5S6JK11fAaw

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Generated by Claude Code

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud