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/api/admin/series.post.js

@@ -1,12 +1,14 @@
 import Series from '../../models/series.js'
 import { connectDB } from '../../utils/mongoose.js'
+import { requireAdmin } from '../../utils/auth.js'
 
 export default defineEventHandler(async (event) => {
   try {
+    const admin = await requireAdmin(event)
     await connectDB()
-    
+
     const body = await readBody(event)
-    
+
     // Validate required fields
     if (!body.id || !body.title || !body.description) {
       throw createError({
@@ -14,7 +16,7 @@ export default defineEventHandler(async (event) => {
         statusMessage: 'Series ID, title, and description are required'
       })
     }
-    
+
     // Create new series
     const newSeries = new Series({
       id: body.id,
@@ -22,7 +24,7 @@ export default defineEventHandler(async (event) => {
       description: body.description,
       type: body.type || 'workshop_series',
       totalEvents: body.totalEvents || null,
-      createdBy: 'admin' // TODO: Get from authentication
+      createdBy: admin.email
     })
     
     await newSeries.save()