feat: scaffold Antonym fashion store

Anonymous Bitcoin-only fashion e-commerce with:
- Vue 3 + Tailwind 4 frontend with glassmorphism dark/light design system
- Express 5 + SQLite backend with BTCPay Server integration
- Nostr identity (NIP-07/keypair) for anonymous purchase tracking
- ChaCha20-Poly1305 encrypted shipping addresses
- Admin panel with order/product/stock management
- SVG logo splash animation with clip-path reveal
- 5 seeded products across 4 categories

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/middleware/validate.ts

@@ -0,0 +1,20 @@
+import type { Request, Response, NextFunction } from 'express'
+
+export function requireBody(...fields: string[]) {
+  return (req: Request, res: Response, next: NextFunction): void => {
+    const missing = fields.filter((f) => req.body[f] === undefined || req.body[f] === null)
+    if (missing.length > 0) { res.status(400).json({ error: { code: 'MISSING_FIELDS', message: `Missing required fields: ${missing.join(', ')}` } }); return }
+    next()
+  }
+}
+
+export function sanitizeString(val: unknown): string {
+  if (typeof val !== 'string') return ''
+  return val.trim().slice(0, 10_000)
+}
+
+export function sanitizeInt(val: unknown): number | null {
+  const n = Number(val)
+  if (!Number.isInteger(n) || n < 0) return null
+  return n
+}