feat(flywheel): few-shot 在线检索注入打通风险规则编译链路

- 新增 FewShotStore：独立 Qdrant collection few_shot_samples，向量 upsert/search/delete，
  全程失败降级不阻塞主链路
- 新增 FewShotIngestionService：RiskObservation confirmed/false_positive → FewShotSample +
  向量，带 sample_key 幂等去重
- 新增 FewShotRetriever：按 case 特征检索相似历史样本，去重 + token 预算 + 单条字符上限裁剪
- risk_observations.create_feedback commit 后挂 hook 自动入库，带 feature flag 和 try/except 兜底
- risk_rule_generation_prompt 新增 few_shot_samples 可选参数，合并进 examples 并标
  source=historical_confirmed；risk_rule_generation 构造 prompt 前调 retriever，失败降级为空

server/src/app/services/risk_rule_generation_prompt.py

@@ -14,10 +14,15 @@ def build_risk_rule_compiler_messages(
     expense_category_label: str,
     natural_language: str,
     available_fields: list[dict[str, Any]],
+    few_shot_samples: list[dict[str, Any]] | None = None,
 ) -> list[dict[str, str]]:
     """构造自然语言规则编译提示词。
 
     大模型只负责把业务语言拆成“语义计划”，后端会校验字段、操作符和模板。
+
+    ``few_shot_samples`` 是从已确认历史样本中检索出来的相似案例，会被合并进
+    ``examples`` 字段并标注 ``source: "historical_confirmed"``，让编译器参考
+    过往人工结论。传 ``None`` 或空列表时行为与历史完全一致（向后兼容）。
     """
 
     schema = {
@@ -161,6 +166,20 @@ def build_risk_rule_compiler_messages(
             },
         }
     ]
+    historical_examples: list[dict[str, Any]] = []
+    if few_shot_samples:
+        for sample in few_shot_samples:
+            historical_examples.append(
+                {
+                    "source": "historical_confirmed",
+                    "label": sample.get("label"),
+                    "domain": sample.get("domain") or "",
+                    "risk_type": sample.get("risk_type") or "",
+                    "conclusion": sample.get("conclusion") or "",
+                    "context": sample.get("context") or {},
+                }
+            )
+    merged_examples = historical_examples + examples
     return [
         {
             "role": "system",
@@ -186,7 +205,7 @@ def build_risk_rule_compiler_messages(
                     "natural_language": natural_language,
                     "available_fields": available_fields,
                     "required_json_shape": response_schema,
-                    "examples": examples,
+                    "examples": merged_examples,
                 },
                 ensure_ascii=False,
             ),