fix(cma): action plan entity_id at the three residual construction sites

alert-to-plan, deviation-push review topic and AI-suggestion-to-plan built ActionPlan(...) without entity_id, so non-e1 sessions wrote rows with the model default 1 and entity_id stayed untrustworthy on those paths. Write the session entity at all three sites, scope the deviation-push topic dedupe by entity (a foreign same-title topic no longer suppresses the session entity's own topic), and require the applied suggestion to belong to the session entity. Adds 7 regression tests (both directions + cross-entity negative controls + auth floor).

backend/app/api/ai_suggestions.py

@@ -238,6 +238,7 @@ def _apply_action_plan(db: Session, sug: AISuggestion, params: dict, current_use
             due_date = None
 
     plan = ActionPlan(
+        entity_id=sug.entity_id,   # 2026-09-18 派生单: 写建议归属账套（=会话账套，端点已校验）
         kpi_id=kpi_id,
         title=title,
         description=params.get("description") or sug.content or f"由AI建议 #{sug.id} 生成: {sug.title}",
@@ -340,6 +341,7 @@ def apply_suggestion(
     suggestion_id: int,
     data: dict,
     db: Session = Depends(get_db),
+    entity_id: int = Depends(get_entity_id),
     current_user=Depends(require_auth),
 ):
     """应用建议：改KPI目标 / 调预算 / 建行动方案（写库+操作日志留痕）
@@ -349,7 +351,10 @@ def apply_suggestion(
       {"action": "budget_adjust", "period": "2026-09", "budget_value": 100000}
       {"action": "action_plan", "title": "...", "assignee": "...", "priority": "high", "due_date": "2026-09-30"}
     """
-    sug = db.query(AISuggestion).filter(AISuggestion.id == suggestion_id).first()
+    sug = db.query(AISuggestion).filter(
+        AISuggestion.id == suggestion_id,
+        AISuggestion.entity_id == entity_id,   # 2026-09-18 派生单: 建议须归属会话账套
+    ).first()
     if not sug:
         raise HTTPException(404, "建议不存在")
     if sug.status == "applied":