test: add Stage 1 lib and Stage 2 services test coverage

Add comprehensive unit tests for:
- lib layer: config, device-fingerprint, errors, storage, hooks/useBreadcrumbs, http
- services layer: devices, login-logs, operation-logs, permissions, profile, roles, settings, stats, import-export

All 491 tests pass across 74 test files.

frontend/admin/src/services/stats.test.ts

@@ -0,0 +1,49 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+
+const getMock = vi.fn()
+
+vi.mock('@/lib/http/client', () => ({
+  get: getMock,
+}))
+
+describe('stats service', () => {
+  beforeEach(() => {
+    getMock.mockReset()
+  })
+
+  it('gets dashboard stats', async () => {
+    const mockStats = {
+      total_users: 100,
+      active_users: 75,
+      new_users_today: 5,
+      total_devices: 200,
+      trusted_devices: 150,
+    }
+
+    getMock.mockResolvedValue(mockStats)
+
+    const { getDashboardStats } = await import('./stats')
+    const result = await getDashboardStats()
+
+    expect(getMock).toHaveBeenCalledWith('/admin/stats/dashboard')
+    expect(result).toEqual(mockStats)
+  })
+
+  it('gets user stats', async () => {
+    const mockUserStats = {
+      total: 100,
+      active: 75,
+      inactive: 25,
+      verified: 80,
+      unverified: 20,
+    }
+
+    getMock.mockResolvedValue(mockUserStats)
+
+    const { getUserStats } = await import('./stats')
+    const result = await getUserStats()
+
+    expect(getMock).toHaveBeenCalledWith('/admin/stats/users')
+    expect(result).toEqual(mockUserStats)
+  })
+})