Implement OWASP ASVS L1 security remediation (Phases 0-2)

Auth: Add requireAuth/requireAdmin guards with JWT cookie verification,
member status checks (suspended/cancelled = 403), and admin role
enforcement. Apply to all admin, upload, and payment endpoints. Add
role field to Member model.

CSRF: Double-submit cookie middleware with client plugin. Exempt
webhook and magic-link verify routes.

Headers: X-Content-Type-Options, X-Frame-Options, X-XSS-Protection,
Referrer-Policy, Permissions-Policy on all responses. HSTS and CSP
(Helcim/Cloudinary/Plausible sources) in production only.

Rate limiting: Auth 5/5min, payment 10/min, upload 10/min, general
100/min via rate-limiter-flexible, keyed by client IP.

XSS: DOMPurify sanitization on marked() output with tag/attr
allowlists. escapeHtml() utility for email template interpolation.

Anti-enumeration: Login returns identical response for existing and
non-existing emails. Remove 404 handling from login UI components.

Mass assignment: Remove helcimCustomerId from profile allowedFields.

Session: 7-day token expiry, refresh endpoint, httpOnly+secure cookies.

Environment: Validate required secrets on startup via server plugin.
Remove JWT_SECRET hardcoded fallback.

server/utils/auth.js

@@ -0,0 +1,65 @@
+import jwt from 'jsonwebtoken'
+import Member from '../models/member.js'
+import { connectDB } from './mongoose.js'
+
+/**
+ * Verify JWT from cookie and return the decoded member.
+ * Throws 401 if token is missing or invalid.
+ */
+export async function requireAuth(event) {
+  await connectDB()
+
+  const token = getCookie(event, 'auth-token')
+
+  if (!token) {
+    throw createError({
+      statusCode: 401,
+      statusMessage: 'Authentication required'
+    })
+  }
+
+  let decoded
+  try {
+    decoded = jwt.verify(token, useRuntimeConfig().jwtSecret)
+  } catch (err) {
+    throw createError({
+      statusCode: 401,
+      statusMessage: 'Invalid or expired token'
+    })
+  }
+
+  const member = await Member.findById(decoded.memberId)
+
+  if (!member) {
+    throw createError({
+      statusCode: 401,
+      statusMessage: 'Member not found'
+    })
+  }
+
+  if (member.status === 'suspended' || member.status === 'cancelled') {
+    throw createError({
+      statusCode: 403,
+      statusMessage: 'Account is ' + member.status
+    })
+  }
+
+  return member
+}
+
+/**
+ * Verify JWT and require admin role.
+ * Throws 401 if not authenticated, 403 if not admin.
+ */
+export async function requireAdmin(event) {
+  const member = await requireAuth(event)
+
+  if (member.role !== 'admin') {
+    throw createError({
+      statusCode: 403,
+      statusMessage: 'Admin access required'
+    })
+  }
+
+  return member
+}