feat(brief): add crewmate identity disambiguation to ship and scout scaffolds

[BenWilcox8]

Intent

Add one sentence to the ship and scout scaffolds in bin/fm-brief.sh: if this worktree's AGENTS.md is firstmate's own, it is the supervisor job description, not yours; you are a crewmate, your brief governs. Both scaffolds carry the disambiguation sentence. Covered by a new test in tests/fm-brief.test.sh asserting the sentence appears in both ship and scout scaffolds. Acceptance: both scaffolds carry the disambiguation sentence and fm-brief tests pass.

What Changed

• Both the ship and scout scaffolds in bin/fm-brief.sh now carry a crewmate identity disambiguation sentence.
  This sentence tells the crewmate agent that firstmate's own AGENTS.md is the supervisor job description, not the crewmate's brief.
• A new test test_crewmate_identity_disambiguation in tests/fm-brief.test.sh checks that both scaffolds carry this sentence.

Risk Assessment

✅ Low: The change adds a single sentence to two heredocs in bin/fm-brief.sh and a corresponding behavioral test that exercises the real binary and checks its generated output file - minimal, well-scoped, and fully conformant with the stated intent.

Testing

Ran the full fm-brief.test.sh suite (23 tests). The new test exercises both the ship and scout code paths by invoking the real fm-brief.sh script and checking the generated brief.md output file for the disambiguation sentence. All 23 tests pass, including the new targeted test.

Evidence: fm-brief test run output

ok - fm-brief.sh: bash -n succeeds
ok - fm-brief.sh: no heredoc is nested inside a command substitution (Bash 3.2 parse-safe)
ok - fm-brief.sh: --help renders the complete header
ok - fm-brief.sh: no-mistakes/direct-PR/local-only briefs generate cleanly
ok - fm-brief.sh: ship --mode is required and closed-set validated
ok - fm-brief.sh: the explicit ship mode wins over the registered posture
ok - fm-brief.sh: --yolo and scout/secondmate --mode are refused, never silently dropped
ok - fm-brief.sh: faster paths use configured authority without stacked review
ok - fm-brief.sh: no-mistakes DOD keeps its apostrophe prose and bans --yes outright
ok - fm-brief.sh: ship project-memory wording carries the AGENTS.md authoring bar
ok - fm-brief.sh: --herdr-lab emits the complete hard safety contract
ok - fm-brief.sh: --herdr-lab uses its quoted Firstmate-owned helper path
ok - fm-brief.sh: ship and scout scaffolds make omitted Herdr intent fail-visible
ok - fm-brief.sh: the documented {TASK} fill cannot corrupt the Herdr safety gate
ok - fm-brief.sh: Herdr lab contract covers scouts and rejects secondmate misuse
ok - fm-brief.sh: crewmate scaffolds stay signal-free and the charter points at the signal owner
ok - fm-brief.sh: --no-projects scaffolds a project-less charter and guards misuse
ok - fm-brief.sh: marked requests avoid generic acknowledgements and preserve material reporting
ok - fm-brief.sh: relative directory inputs ignore CDPATH, render stable absolute charter paths, or fail loudly
ok - fm-brief.sh: custom pause verb renders in every scaffold
ok - fm-brief.sh: investigation and visual-review completions load the shared decision policy
ok - fm-brief: scout and secondmate code paths still scaffold well-formed briefs
ok - fm-brief.sh: ship and scout scaffolds carry the crewmate identity disambiguation sentence

Pipeline

Updates from git push no-mistakes

✅ **intent** - passed

✅ No issues found.

✅ **Rebase** - passed

✅ No issues found.

✅ **Review** - passed

✅ No issues found.

✅ **Test** - passed

✅ No issues found.

• bash tests/fm-brief.test.sh - full suite including new test_crewmate_identity_disambiguation which invokes fm-brief.sh for both ship and scout paths and asserts the generated brief files contain the disambiguation sentence

✅ **Document** - passed

✅ No issues found.

✅ **Lint** - passed

✅ No issues found.

✅ **Push** - passed

✅ No issues found.