feat(platform): tini as PID 1, Hypercorn, a log-level setting, the image on CI's Python, an airgapped boot gate before push (#5159)

- Dockerfile: python:3.14-slim, the Python CI tests on (was 3.13). tini from
  apt is PID 1 (ENTRYPOINT tini -- entrypoint.sh): it reaps the zombies ssh
  and ansible leave and forwards SIGTERM.
- cli: Hypercorn's serve() with one worker (run, stream and scheduler state is
  in-process), a 10 s graceful timeout, and SIGTERM/SIGINT as the shutdown
  trigger. Access and error lines go through Steward's logging. --debug keeps
  Quart's reloading dev server.
- Logging: steward/core/logging_setup.py installs one root handler before
  anything logs (until now a library's basicConfig on import was the only
  configuration). Its level is the `log.level` setting (DEBUG/INFO/WARNING/
  ERROR, default INFO), applied at boot and on save in Settings → General.
- CI publish: build, then "The image boots with no internet" (rule 164,
  snippet #3552), then push, so a broken image never reaches a tag (rule 177).
  On an --internal network with its own Postgres, the image must migrate and
  answer /health, run tini as PID 1, serve first-run setup with its assets
  from /static and no third-party host, and exit 0 on SIGTERM. Logs and
  clean-up run always.

Tests: tests/core/test_logging_setup.py; the smoke step itself.
Not in this commit: the dependency lockfile (it conflicts with rule 154 and
is waiting on the operator).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Dockerfile

@@ -1,4 +1,5 @@
-FROM python:3.13-slim
+# The Python CI tests on (ci-python:3.14), so the image runs what was tested.
+FROM python:3.14-slim
 
 RUN DEBIAN_FRONTEND=noninteractive apt-get update \
     && DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends \
@@ -12,6 +13,9 @@ RUN DEBIAN_FRONTEND=noninteractive apt-get update \
         sshpass \
         # git — clones and pulls Ansible git sources (Settings > Ansible)
         git \
+        # tini — PID 1: reaps the zombies ssh and ansible leave behind and
+        # forwards SIGTERM to Steward so a stop is a graceful shutdown
+        tini \
     && rm -rf /var/lib/apt/lists/*
 
 # Upgrade pip to suppress the version notice
@@ -44,5 +48,5 @@ RUN useradd -m -u 1000 app \
 
 EXPOSE 5000
 
-ENTRYPOINT ["/entrypoint.sh"]
+ENTRYPOINT ["/usr/bin/tini", "--", "/entrypoint.sh"]
 CMD ["steward", "--host", "0.0.0.0", "--port", "5000"]