fix(correctness): 并发/事务/实体/时区/状态一致性修复

由 OCR（open-codereview.ai，deepseek-v4-flash）审查驱动修复：
- wallets 原子扣款防 double-spend；refund 条件更新幂等；findTransactions 分页
- financial/imports/occupancies/attendance 事务与 advisory lock；重复生成/提交幂等
- 矛盾校验器、日期区间、实体双映射/DECIMAL/nullable、时区统一（china-time）
- rbac-seed 防重激活、exam 权限恢复、状态一致性、路由顺序、N+1/IN 分块等性能项

Reviewed-by: OCR (open-codereview.ai)

apps/server/src/entities/bill.entity.ts

@@ -24,22 +24,57 @@ export class Bill {
   @Column({ name: 'period_end', type: 'date' })
   periodEnd: string;
 
-  @Column({ name: 'shared_amount', type: 'decimal', precision: 10, scale: 2, default: 0 })
+  @Column({
+    name: 'shared_amount',
+    type: 'decimal',
+    precision: 10,
+    scale: 2,
+    default: 0,
+    transformer: { to: (v: number) => v, from: (v: string | null) => (v == null ? v : Number(v)) },
+  })
   sharedAmount: number;
 
-  @Column({ name: 'personal_amount', type: 'decimal', precision: 10, scale: 2, default: 0 })
+  @Column({
+    name: 'personal_amount',
+    type: 'decimal',
+    precision: 10,
+    scale: 2,
+    default: 0,
+    transformer: { to: (v: number) => v, from: (v: string | null) => (v == null ? v : Number(v)) },
+  })
   personalAmount: number;
 
-  @Column({ name: 'total_amount', type: 'decimal', precision: 10, scale: 2, default: 0 })
+  @Column({
+    name: 'total_amount',
+    type: 'decimal',
+    precision: 10,
+    scale: 2,
+    default: 0,
+    transformer: { to: (v: number) => v, from: (v: string | null) => (v == null ? v : Number(v)) },
+  })
   totalAmount: number;
 
   @Column({ type: 'varchar', length: 30, default: 'batch' })
   source: 'batch' | 'student_utility';
 
-  @Column({ name: 'paid_amount', type: 'decimal', precision: 10, scale: 2, default: 0 })
+  @Column({
+    name: 'paid_amount',
+    type: 'decimal',
+    precision: 10,
+    scale: 2,
+    default: 0,
+    transformer: { to: (v: number) => v, from: (v: string | null) => (v == null ? v : Number(v)) },
+  })
   paidAmount: number;
 
-  @Column({ name: 'outstanding_amount', type: 'decimal', precision: 10, scale: 2, default: 0 })
+  @Column({
+    name: 'outstanding_amount',
+    type: 'decimal',
+    precision: 10,
+    scale: 2,
+    default: 0,
+    transformer: { to: (v: number) => v, from: (v: string | null) => (v == null ? v : Number(v)) },
+  })
   outstandingAmount: number;
 
   @Column({ type: 'varchar', length: 20, default: 'unpaid' })