feat(boss): opt-in spec auto-sign via adversarial spec-skeptic panel

Add `pipeline.boss.spec_auto_sign` (default off). With it on, a /boss
run may sign a spec in the user's place — but only through a gate built
to never rely on the orchestrator's own confidence: all objective gates
green (precondition, parse, grounding-check PASS with no human override)
AND a unanimous five-lens adversarial spec-skeptic panel (criterion,
grounding, scope-fork, ambiguity, plan-readiness). Any single BLOCK
falls back to the human sign-off pause.

On a clean sign the orchestrator commits the spec ((boss-signed) in the
subject), fires a mandatory informational-with-veto notify, and proceeds
to planner without stopping. A later veto is a forward correction, never
a history rewind.

- new agent: specify/agents/spec-skeptic.md (read-only, one lens per dispatch)
- specify Step 6 + Iron Law: approval may come from the auto-sign gate,
  never from model self-confidence
- boss: third notify category, §"Spec auto-sign", rationalisations, red flags
- profile-schema + template: the opt-in slot
- pipeline.md, agent-template.md, README: the auto-sign path documented

docs/agent-template.md

@@ -74,7 +74,7 @@ plugin's agent path is enough disambiguator).
 
 Examples: `architect`, `bencher`, `debugger`, `implementer`,
 `tester`, `fieldtester`, `docwriter`, `grounding-check`,
-`plan-recon`, `spec-reviewer`, `quality-reviewer`,
+`spec-skeptic`, `plan-recon`, `spec-reviewer`, `quality-reviewer`,
 `implement-orchestrator`.
 
 ### `description`
@@ -93,7 +93,7 @@ agents.
 Common tool sets:
 
 - Read-only review (architect, spec-reviewer, quality-reviewer,
-  grounding-check, plan-recon): `Read, Glob, Grep, Bash`
+  grounding-check, spec-skeptic, plan-recon): `Read, Glob, Grep, Bash`
 - Implementation (implementer, tester, debugger, docwriter,
   fieldtester, bencher): `Read, Edit, Write, Bash, Glob, Grep`
 - Orchestrator (implement-orchestrator): `Read, Edit, Write,