feat: implement subscription web dashboard with admin controls (#215)

[Itodo-S]

Summary

Closes #215 — extends the admin dashboard service with audit log filtering and comprehensive test coverage.

Changes

src/services/adminDashboardService.ts

• Added filterAuditLog(log, filter) — filters the audit event log by any combination of resourceType, action, and actorId (all criteria are AND-ed)
• Exported AuditLogFilter interface

src/services/__tests__/adminDashboardService.test.ts

• Expanded from 4 to 25+ test cases covering all RBAC operations:
  • getAdminDashboardData — shape, immutability
  • toggleMerchantStatus — admin suspends/activates, non-admin blocked, no mutation
  • upsertSubscription — role gating (admin/analyst can create, support cannot)
  • cycleSubscriptionStatus — all status transitions, support blocked
  • deleteSubscription — admin removes, non-admin blocked
  • bulkUpdateSubscriptions — selective pause, support blocked, empty selection
  • updateUserRole — role cycling (viewer→analyst→support→viewer), non-admin blocked
  • filterAuditLog — filter by resourceType/action/actorId, multi-criteria AND, empty filter, no-match

Acceptance criteria coverage

• Merchant management interface — toggleMerchantStatus RBAC
• Subscription CRUD operations — create, cycle status, delete, bulk update
• Analytics and reporting — getAdminDashboardData returns analytics snapshot
• Implement bulk operations — bulkUpdateSubscriptions
• User management — updateUserRole with role cycling
• Implement audit logging — filterAuditLog for drill-down queries
• Role-based access for dashboard — all operations gated by DashboardRole

Test plan

• jest --testPathPattern=adminDashboardService — all tests pass