Fix duplicate session billing and align pricing with DeepSeek ×3.

Serialize billSessionUsage with row locks, expose rates on recharge, add compensation script and admin usage views.

Co-authored-by: Cursor <cursoragent@cursor.com>

billing.mjs

@@ -1,11 +1,29 @@
+// DeepSeek V4 Flash 公开价（$/1M tokens，cache-miss 输入）；见 api-docs.deepseek.com
+export const DEEPSEEK_FLASH_INPUT_USD_PER_1M = 0.14;
+export const DEEPSEEK_FLASH_OUTPUT_USD_PER_1M = 0.28;
+export const DEEPSEEK_BILLING_MARKUP = 3;
+
+function deepSeekFlashCentsPer1k(usdPer1M, usdCnyRate) {
+  return (usdPer1M / 1000) * usdCnyRate * 100 * DEEPSEEK_BILLING_MARKUP;
+}
+
 export function loadBillingConfig() {
   // 默认按人民币分（CNY cents）计费；仅当 H5_USE_BACKEND_COST=1 时才用上游 USD 成本换算。
   const useBackendCost = process.env.H5_USE_BACKEND_COST === '1';
+  const usdCnyRate = Number(process.env.H5_USD_CNY_RATE ?? 7.2);
+  const defaultInputCentsPer1k = deepSeekFlashCentsPer1k(
+    DEEPSEEK_FLASH_INPUT_USD_PER_1M,
+    usdCnyRate,
+  );
+  const defaultOutputCentsPer1k = deepSeekFlashCentsPer1k(
+    DEEPSEEK_FLASH_OUTPUT_USD_PER_1M,
+    usdCnyRate,
+  );
   return {
     useBackendCost,
-    usdCnyRate: Number(process.env.H5_USD_CNY_RATE ?? 7.2),
-    inputCentsPer1k: Number(process.env.H5_BILL_INPUT_CENTS_PER_1K ?? 2),
-    outputCentsPer1k: Number(process.env.H5_BILL_OUTPUT_CENTS_PER_1K ?? 6),
+    usdCnyRate,
+    inputCentsPer1k: Number(process.env.H5_BILL_INPUT_CENTS_PER_1K ?? defaultInputCentsPer1k),
+    outputCentsPer1k: Number(process.env.H5_BILL_OUTPUT_CENTS_PER_1K ?? defaultOutputCentsPer1k),
     minBillCents: Number(process.env.H5_MIN_BILL_CENTS ?? 1),
   };
 }