Clarify ambiguous briefs before drafting sailing orders

[harrymunro]

Summary

• Adds an instruction to Step 1 (Issue Sailing Orders) for the admiral to review the user's brief for ambiguity and ask clarifying questions before proceeding.

Test plan

• Invoke /nelson with a vague brief and verify the admiral asks clarifying questions before drafting sailing orders
• Invoke /nelson with a clear brief and verify it proceeds without unnecessary questions