Show the Epic merge plan

Output contract: Relay requested CLI fields or output faithfully; preserve warnings/errors and only the explanations required below. For suggested actions, pair Shell with the returned Copilot command; honor commandGuidance. If absent, say "Copilot: no verified equivalent"; never invent a slash command.

Boundary: no Story required; cwd=opened Git root or verified repositoryPath from singularity-flow workspace current --json; refuse if neither resolves; never search $HOME/parents.

1. Run singularity-flow epic merge-plan --epic <EPIC-KEY> --json.
2. Display Story order, repository, blocking flag, dependencies, current state, and the next merge candidate.
3. Clearly separate unreachable, blocked, and ready Stories.
4. Report whether every blocking Story has merged and whether the Epic branch is ready.
5. This is read-only; do not merge, rebase, or push.