feat: 添加可配置场景注册表与规则引擎

- 新增场景基类、配置加载、注册表与原语模块
- 添加 r10_refund_split 规则及场景 JSON Schema
- 扩展 scan 引擎与 scenarios API
- 新增场景注册表/配置/集成测试
- 更新前端 App、api、labels 支持新场景

backend/app/scenarios/split_contract.py

@@ -10,6 +10,9 @@ from __future__ import annotations
 
 from dataclasses import dataclass, field
 
+from app.scenarios.base import BaseScenario, ClueDraft, ScanOutcome
+from app.scenarios.registry import register_scenario
+
 
 @dataclass
 class ContractRecord:
@@ -76,3 +79,58 @@ def build_rationale(finding: SplitFinding, threshold: float, shared_controller:
     else:
         parts.append("建议进一步穿透客户关联关系以确认是否同一实控人。")
     return "".join(parts)
+
+
+@register_scenario
+class SplitContractScenario(BaseScenario):
+    """场景一拆单检测的插件封装：检测→评分→产出线索草稿。
+
+    数据通过构造注入（兼容现有 seed/测试的数据流）；后续可改为从 session 自取数，
+    接口保持不变。
+    """
+
+    code = "R8"
+    title = "疑似政企拆单规避审批"
+    risk_domain = "收入"
+    label = "政企拆单"
+    score_threshold = 0.0  # 命中即出线索（与原 run_split_contract_scan 的 score>0 一致）
+
+    def __init__(
+        self,
+        contracts: list[ContractRecord],
+        approval_threshold: float,
+        shared_controller: bool = False,
+    ) -> None:
+        self.contracts = contracts
+        self.approval_threshold = approval_threshold
+        self.shared_controller = shared_controller
+
+    def scan(self, session, *, data_version_id=None) -> ScanOutcome:
+        finding = detect_threshold_edge(self.contracts, self.approval_threshold)
+        score = split_risk_score(finding, self.shared_controller)
+        drafts: list[ClueDraft] = []
+        if score > 0:
+            drafts.append(
+                ClueDraft(
+                    score=score,
+                    rationale=build_rationale(
+                        finding, self.approval_threshold, self.shared_controller
+                    ),
+                    evidence={
+                        "near_threshold_contracts": [
+                            c.contract_id for c in finding.near_threshold
+                        ],
+                        "edge_ratio": finding.ratio,
+                        "near_threshold_amount": finding.total_amount,
+                        "approval_threshold": self.approval_threshold,
+                        "shared_controller": self.shared_controller,
+                    },
+                    subjects={
+                        "customers": sorted(
+                            {c.customer_key for c in finding.near_threshold}
+                        )
+                    },
+                    amount_involved=finding.total_amount,
+                )
+            )
+        return ScanOutcome(scanned_count=len(self.contracts), drafts=drafts)