fix: ensure all timestamps use UTC timezone

- Add NowFunc to GORM config for UTC auto-generated timestamps
- Add .UTC() to all time.UnixMilli() calls in trader files
- Add .UTC() to all time.Now() calls in store and api files
- Fix TypeScript unused imports in frontend

web/src/pages/TraderDashboardPage.tsx

@@ -1,5 +1,4 @@
 import { useEffect, useState, useRef } from 'react'
-import { motion, AnimatePresence } from 'framer-motion'
 import { mutate } from 'swr'
 import { api } from '../lib/api'
 import { ChartTabs } from '../components/ChartTabs'