bug(unic-archon-dlc): /setup assumes a non-Gitflow trunk is called main #653

Problem

/unic-archon-dlc:setup assumes the trunk of a non-Gitflow repository is called main.

apps/claude-code/unic-archon-dlc/commands/setup.md derives the base a branching model implies as develop for gitflow and main for anything else, and warns when worktree.baseBranch disagrees with it. In a repository whose trunk is master, or any other name, /setup prints a false warning and suggests baseBranch: main. If the operator follows it, every run fails, because archon workflow run --base refuses a branch that is missing on the remote. The failure is visible, so the cost is a wasted run and a confused operator, not a wrong merge.

Criterion 8 of #505 fixes the rule as written, so PR #650 keeps it. It was found by the round 2 silent-failure review of that PR.

Acceptance criteria

1. For a non-Gitflow repository, /setup takes the trunk name from the remote's default branch, not from a hard-coded main, before it compares it with worktree.baseBranch.
2. When /setup cannot read the remote's default branch, it says so and does not suggest a baseBranch value.
3. A repository whose trunk is master and whose worktree.baseBranch is master gets no warning.