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>

src/types.ts

@@ -141,6 +141,8 @@ export type BillingConfig = {
   tiersCents: number[];
   minRechargeCents: number;
   balanceCents: number;
+  inputCentsPer1k: number;
+  outputCentsPer1k: number;
 };
 
 export type JsapiPayParams = {
@@ -619,6 +621,19 @@ export type UsageRecord = {
   createdAt: number;
 };
 
+export type UsageTotals = {
+  requestCount: number;
+  inputTokens: number | null;
+  outputTokens: number | null;
+  totalTokens: number;
+  costCents: number;
+};
+
+export type UsageSummary = {
+  allTime: UsageTotals;
+  last24h: UsageTotals;
+};
+
 export type BalanceUpdate = {
   balanceCents: number;
   tokensUsed?: number;