Withdraw unic-archon-dlc from the marketplace catalogue #679

Why

The maintainer decided on 2026-10-30 to leave Archon (#677). The DLC moves to a new plugin. Until it exists, no new project should start on unic-archon-dlc, because every new project is one more to support and later migrate.

Both catalogues read .claude-plugin/marketplace.json on main: Claude Code's marketplace, and the Unic marketplace, which the ingest workflow updates on every push to main. The Unic card cannot be withdrawn by hand, because a pipeline pushed it. It disappears only when the push stops sending it. So the entry leaves the file.

The cost is accepted: after this lands, /plugin install unic-archon-dlc@unic-agent-plugins fails for a project that adds the marketplace at main. Projects that already run the plugin keep their installed copy.

Acceptance criteria

1. On main, .claude-plugin/marketplace.json has no unic-archon-dlc entry. Every other entry is byte-identical to before.
2. The same holds on develop.
3. On both branches, the root README.md no longer tells a reader to install unic-archon-dlc. Its row in the plugin table is gone, and one sentence says the plugin was withdrawn from the catalogue on 2026-10-30 and links Does the DLC stay on Archon, or move to a new plugin that does not run on it? #677.
4. The plugin is marked deprecated where a GitHub reader sees it. apps/claude-code/unic-archon-dlc/.claude-plugin/plugin.json has a description that starts with [DEPRECATED — being replaced, see #677], the way pr-review marks itself. The plugin's own README.md opens with one sentence that says the same and links Does the DLC stay on Archon, or move to a new plugin that does not run on it? #677. Nothing else under apps/claude-code/unic-archon-dlc/ changes. No version bump, no tag.
5. Delivered as a hotfix: one hotfix/* branch from main, with one pull request to main and one to develop.
6. After the merge to main, the ingest run reports one removed artefact, and the Unic marketplace no longer lists unic-agents-plugins/unic-archon-dlc.

Criterion 6 is checked by the orchestrator after the merge, not by the pull request.

Amended 2026-10-30

The maintainer chose a mix: remove the plugin from the catalogue so no new project starts on it, and mark it deprecated so a reader on GitHub sees why. Criterion 4 changed from "nothing under the plugin changes" to the deprecation marks. The other criteria are unchanged.