Core image smoke: boot the image and pair a Panel with it

[qcentic-dev]

Part of #23. Spec: ADR 0016 — The 0.1.0 shape, clauses D36.

Phase 2 — Images and container
Blocked by: #37, #39, #40, #45
Blocks: #61

What

Replaces panel-e2e-core-in-a-box, and it is a straight upgrade: that job needed --privileged and the host cgroup to boot a systemd fixture, and that fixture is deleted. This makes the same assertion against the bytes that actually ship.

It does not replace the installer e2e (T19) and must not be argued to. They share nothing but the daemon binary: different arrival (docker pull vs checksum-verified curl | bash), different PID 1, different service management, different install location, and lifecycle verbs that are deliberately degraded in the image.

Done when

• Builds deploy/core.Dockerfile, boots it, and a Panel pairs with it end to end — no privileged container anywhere
• Asserts restart is a no-op for pairing, and down -v unpairs (T11)
• Asserts the refused verbs refuse and name the Docker equivalent (T10)
• Asserts tini is PID 1 and the daemon is PID 2
• Runs the Trivy gate from T9 in the same job
• panel-e2e-core-in-a-box and its fixture are deleted in the same PR

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_{Decisions are locked in ADR 0016. If this ticket needs one changed, amend the ADR in the same PR — do not decide it in a comment.}