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.

app/plugins/csrf.client.js

@@ -0,0 +1,23 @@
+export default defineNuxtPlugin(() => {
+  const safeMethods = new Set(['GET', 'HEAD', 'OPTIONS'])
+
+  globalThis.$fetch = globalThis.$fetch.create({
+    onRequest({ options }) {
+      const method = (options.method || 'GET').toUpperCase()
+      if (safeMethods.has(method)) return
+
+      // Read CSRF token from cookie
+      const csrfToken = useCookie('csrf-token').value
+      if (csrfToken) {
+        options.headers = options.headers || {}
+        if (options.headers instanceof Headers) {
+          options.headers.set('x-csrf-token', csrfToken)
+        } else if (Array.isArray(options.headers)) {
+          options.headers.push(['x-csrf-token', csrfToken])
+        } else {
+          options.headers['x-csrf-token'] = csrfToken
+        }
+      }
+    }
+  })
+})