feat(reports): 企业合规报表（后端聚合 + CSV 导出 + 前端页面） (#82)

新增合规报表：ReportService 逐任务聚合备份合规证据（成功率/最近成功/SLA 判定/加密/受保护量）+ JSON/CSV API；前端新增 /reports 页面（汇总卡片+明细表+CSV 导出）。后端 go test、前端 tsc+vite、端到端路由验证均通过。

web/src/types/reports.ts

@@ -0,0 +1,40 @@
+export type ComplianceRisk = 'ok' | 'at_risk' | 'not_applicable'
+
+export interface ComplianceTaskRow {
+  taskId: number
+  taskName: string
+  type: string
+  enabled: boolean
+  nodeName: string
+  cronExpr: string
+  encrypted: boolean
+  retentionDays: number
+  slaHoursRpo: number
+  totalRuns: number
+  successes: number
+  failures: number
+  successRate: number
+  lastStatus: string
+  lastRunAt?: string
+  lastSuccessAt?: string
+  protectedBytes: number
+  compliant: boolean
+  risk: ComplianceRisk
+}
+
+export interface ComplianceSummary {
+  totalTasks: number
+  enabledTasks: number
+  compliantTasks: number
+  atRiskTasks: number
+  encryptedTasks: number
+  overallSuccessRate: number
+  totalProtectedBytes: number
+}
+
+export interface ComplianceReport {
+  generatedAt: string
+  rangeDays: number
+  summary: ComplianceSummary
+  tasks: ComplianceTaskRow[]
+}