feat: Phase 2 — RAG integration in Requirements + DSFA Draft

Add legal context enrichment from Qdrant vector corpus to the two
highest-priority modules (Requirements AI assistant and DSFA drafting
engine).

Go SDK:
- Add SearchCollection() with collection override + whitelist validation
- Refactor Search() to delegate to shared searchInternal()

Python backend:
- New ComplianceRAGClient proxying POST /sdk/v1/rag/search (error-tolerant)
- AI assistant: enrich interpret_requirement() and suggest_controls() with RAG
- Requirements API: add ?include_legal_context=true query parameter

Admin (Next.js):
- Extract shared queryRAG() utility from chat route
- Inject RAG legal context into v1 and v2 draft pipelines

Tests for all three layers (Go, Python, TypeScript shared utility).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend-compliance/compliance/api/routes.py

@@ -177,8 +177,12 @@ async def get_regulation_requirements(
 
 
 @router.get("/requirements/{requirement_id}")
-async def get_requirement(requirement_id: str, db: Session = Depends(get_db)):
-    """Get a specific requirement by ID."""
+async def get_requirement(
+    requirement_id: str,
+    include_legal_context: bool = Query(False, description="Include RAG legal context"),
+    db: Session = Depends(get_db),
+):
+    """Get a specific requirement by ID, optionally with RAG legal context."""
     from ..db.models import RequirementDB, RegulationDB
 
     requirement = db.query(RequirementDB).filter(RequirementDB.id == requirement_id).first()
@@ -187,7 +191,7 @@ async def get_requirement(requirement_id: str, db: Session = Depends(get_db)):
 
     regulation = db.query(RegulationDB).filter(RegulationDB.id == requirement.regulation_id).first()
 
-    return {
+    result = {
         "id": requirement.id,
         "regulation_id": requirement.regulation_id,
         "regulation_code": regulation.code if regulation else None,
@@ -214,6 +218,33 @@ async def get_requirement(requirement_id: str, db: Session = Depends(get_db)):
         "source_section": requirement.source_section,
     }
 
+    if include_legal_context:
+        try:
+            from ..services.rag_client import get_rag_client
+            from ..services.ai_compliance_assistant import AIComplianceAssistant
+
+            rag = get_rag_client()
+            assistant = AIComplianceAssistant()
+            query = f"{requirement.title} {requirement.article or ''}"
+            collection = assistant._collection_for_regulation(regulation.code if regulation else "")
+            rag_results = await rag.search(query, collection=collection, top_k=3)
+            result["legal_context"] = [
+                {
+                    "text": r.text,
+                    "regulation_code": r.regulation_code,
+                    "regulation_short": r.regulation_short,
+                    "article": r.article,
+                    "score": r.score,
+                    "source_url": r.source_url,
+                }
+                for r in rag_results
+            ]
+        except Exception as e:
+            logger.warning("Failed to fetch legal context for %s: %s", requirement_id, e)
+            result["legal_context"] = []
+
+    return result
+
 
 @router.get("/requirements", response_model=PaginatedRequirementResponse)
 async def list_requirements_paginated(