feat(navigator): Product Regulatory Navigator as a thin missing-facts layer

Step 2 of the convergence sequence. The Navigator sits over the
CanonicalProductRegulatoryProfile (prefilled from company-profile / ProductWizard)
and reports ONLY which facts are still missing + prioritized questions to collect
them. It decides which facts are needed, NEVER what applies — that stays with the
Scope Engine (step 3). No regulation logic, no UI, no Go, no RAG.

- NavigatorQuestion (interaction type, NOT a compliance-meta-model class — freeze
  v1.0 untouched): question_id, target_field, label, why_needed,
  regulatory_domains_unblocked (static metadata), answer_type, options, priority.
- QUESTION_CATALOG: 12 questions over canonical gaps — P0 (markets, role,
  lifecycle, machine/component), P1 (radio, usage-data, security-function,
  environmental wastewater/air/chemicals triggers), P2 (structured BOM).
- engine: navigate() -> missing_facts + suggested_questions (priority-sorted) +
  completeness_summary (ready_for_scope = no P0 missing); apply_answers() ->
  updated profile. Pure field-presence; no scope import.
- 8 tests: <=10 questions for a filled company-profile, known facts not re-asked,
  environmental = trigger questions only (no law evaluation), apply round-trip,
  P0 ordering, ready_for_scope. 41 tests green, mypy clean, LOC ok.

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

backend-compliance/compliance/navigator/__init__.py

@@ -0,0 +1,29 @@
+"""Product Regulatory Navigator — thin missing-facts layer.
+
+Sits above the CanonicalProductRegulatoryProfile (prefilled from company-profile /
+ProductWizard) and reports only which facts are still missing + prioritized
+questions to collect them. It decides which facts are needed, NOT what regulation
+applies — that stays with the Scope Engine (step 3). No regulation logic, no UI,
+no Go, no RAG.
+"""
+
+from __future__ import annotations
+
+from .engine import CompletenessSummary, NavigatorResult, apply_answers, navigate
+from .questions import (
+    QUESTION_CATALOG,
+    AnswerType,
+    NavigatorQuestion,
+    QuestionPriority,
+)
+
+__all__ = [
+    "navigate",
+    "apply_answers",
+    "NavigatorResult",
+    "CompletenessSummary",
+    "NavigatorQuestion",
+    "AnswerType",
+    "QuestionPriority",
+    "QUESTION_CATALOG",
+]