feat(advisor): Phase 1 — endpoint backward-compat (keep breakpilot-workspace working)

The advisor endpoint now serves two shapes off one orchestration:
- new FE ({question}) -> v3 JSON contract (clarity/answer/evidence/citations/...).
- legacy consumer ({message}, e.g. breakpilot-workspace which reads a text stream and
  persists raw bytes) -> plain-text stream of the L2 answer (clean prose, no [n] markup,
  no clarify gate). isLegacyRequest() discriminates; answerSystem() gains withCitations.

Prevents the v3 contract from breaking breakpilot-workspace's chat (CLAUDE.md rule #4,
keep every consumer working). No deploy. tsc clean, 13 vitest (incl. isLegacyRequest),
check-loc 0.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

admin-compliance/lib/sdk/advisor/retrieve-mapping.ts

@@ -81,3 +81,11 @@ export function numberedEvidenceForPrompt(evidence: EvidenceUnit[]): string {
     })
     .join('\n\n')
 }
+
+/**
+ * Backward-compat discriminator: legacy consumers (e.g. breakpilot-workspace) send `{message}`
+ * and read a plain-text stream; the new FE sends `{question}` and expects the JSON contract.
+ */
+export function isLegacyRequest(body: { question?: unknown; message?: unknown }): boolean {
+  return body.question == null && typeof body.message === 'string'
+}