feat(epic): add Working Model as required section for epics

Epics now require a "Working Model" section in their description,
in addition to "Success Criteria". This provides clear guidance on
HOW the epic will be executed:

- Owner role: Coordinator vs Implementer
- Delegation target: Polecats, crew, external
- Review process: Approval gates

Closes gt-0lp

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

claude-plugin/commands/epic.md

@@ -24,3 +24,25 @@ Manage epics (large features composed of multiple issues).
 4. Auto-close when done: `bd epic close-eligible`
 
 Epics use parent-child dependencies to track subtasks.
+
+## Epic Template Sections
+
+Epics require two sections in their description:
+
+### Success Criteria
+Define high-level criteria for epic completion. What does "done" look like?
+
+### Working Model
+Define HOW the epic will be executed:
+
+- **Owner role**: Is the assignee a Coordinator (decomposes and delegates) or Implementer (does hands-on work)?
+- **Delegation target**: Who does the work? Polecats? Other crew? External contributors?
+- **Review process**: Who approves completed subtasks? What gates must pass?
+
+Example:
+```markdown
+## Working Model
+- **Owner role**: Coordinator - decompose into subtasks and sling to polecats
+- **Delegation target**: Polecat swarm (3-5 workers)
+- **Review process**: Refinery MQ for each subtask, owner approval for epic closure
+```