Run the /setup 0.30.0 marker migration in a scratch Consumer #651

Problem

PR #649 (for #520) moves the DLC's managed-block markers from unic-archon-dlc:begin / unic-archon-dlc:end to unic-dlc:begin / unic-dlc:end. Step 7 of commands/setup.md migrates an old block in place. The CHANGELOG lists this under ### Breaking for 0.30.0.

AGENTS.md § The quality bar for a prose Box says a change runs where it ships. Nobody has run the migration in a Consumer. If it fails, an upgraded Consumer ends with two blocks in one file, or loses the text after an unterminated old marker.

Acceptance criteria

1. Install unic-archon-dlc 0.30.0 or later from the marketplace into a scratch Consumer outside every clone, and run /setup once for each starting state below. Record each result on this ticket:
   • CLAUDE.md with an old block that is not at the end of the file;
   • a line-based formatter ignore file with an old block;
   • a file that holds both an old block and a new block;
   • a file with an old begin marker and no end marker.
2. In the first three states, each file ends with exactly one block, under unic-dlc markers, and the text outside the block is unchanged. In the fourth, /setup writes nothing to that file and its Step 8 summary reports it as an open item.
3. The comment states the plugin version, the Archon version and the Claude Code version the run used.