feat(db): add usage tracking schema and types

Add database tables for proxy request logs and model pricing.
Extend Provider and error types to support usage statistics.

src/types/usage.ts

@@ -0,0 +1,96 @@
+// 使用统计相关类型定义
+
+export interface TokenUsage {
+  inputTokens: number;
+  outputTokens: number;
+  cacheReadTokens: number;
+  cacheCreationTokens: number;
+}
+
+export interface RequestLog {
+  requestId: string;
+  providerId: string;
+  appType: string;
+  model: string;
+  inputTokens: number;
+  outputTokens: number;
+  cacheReadTokens: number;
+  cacheCreationTokens: number;
+  inputCostUsd: string;
+  outputCostUsd: string;
+  cacheReadCostUsd: string;
+  cacheCreationCostUsd: string;
+  totalCostUsd: string;
+  latencyMs: number;
+  statusCode: number;
+  errorMessage?: string;
+  createdAt: number;
+}
+
+export interface ModelPricing {
+  modelId: string;
+  displayName: string;
+  inputCostPerMillion: string;
+  outputCostPerMillion: string;
+  cacheReadCostPerMillion: string;
+  cacheCreationCostPerMillion: string;
+}
+
+export interface UsageSummary {
+  totalRequests: number;
+  totalCost: string;
+  totalInputTokens: number;
+  totalOutputTokens: number;
+  successRate: number;
+}
+
+export interface DailyStats {
+  date: string;
+  requestCount: number;
+  totalCost: string;
+  totalTokens: number;
+}
+
+export interface ProviderStats {
+  providerId: string;
+  providerName: string;
+  requestCount: number;
+  totalTokens: number;
+  totalCost: string;
+  successRate: number;
+  avgLatencyMs: number;
+}
+
+export interface ModelStats {
+  model: string;
+  requestCount: number;
+  totalTokens: number;
+  totalCost: string;
+  avgCostPerRequest: string;
+}
+
+export interface LogFilters {
+  providerId?: string;
+  model?: string;
+  statusCode?: number;
+  startDate?: number;
+  endDate?: number;
+}
+
+export interface ProviderLimitStatus {
+  providerId: string;
+  dailyUsage: string;
+  dailyLimit?: string;
+  dailyExceeded: boolean;
+  monthlyUsage: string;
+  monthlyLimit?: string;
+  monthlyExceeded: boolean;
+}
+
+export type TimeRange = '7d' | '30d' | '90d';
+
+export interface StatsFilters {
+  timeRange: TimeRange;
+  providerId?: string;
+  appType?: string;
+}