Check the Web port before an offline install

[SaladDay]

What

deploy/install-source.py (offline install):

• D1: a new installation bind-tests --host:--web-port before any image loads, refusing with the same holder hint as oac install (live installation directory named; down --volumes only when its working_dir is gone). After up, a missing published Web port (docker compose port web 8080) fails the run, naming the holder, instead of reporting success on a rerun.
• D3: Console: (saved OAC_PUBLIC_URL) prints on every successful run.
• D4: docker info runs first; no access gives the docker-group message from oac install, plus not-installed / not-running messages.

D2 is out of scope.

Verification

• python3 -m unittest deploy.test_install_source: pass (3 new tests: taken port before image load, docker-group message, rerun without published port + Console on rerun).
• python3 scripts/check-names.py: pass.
• Skipped: no real Docker port-conflict run (covered by the mx evidence in the injection README).

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