feat: reskin admin pages to zine design system

Migrate the entire admin section from the dark guild-* Tailwind theme
to the zine design system (dashed borders, CSS custom properties,
Brygada 1918 + Commit Mono, cream/dark mode palette).

- Replace admin top-nav layout with sidebar matching default layout
- Reskin dashboard, members, events, series management pages
- Reskin events/create and series/create form pages
- Add dev-only test login endpoint (GET /api/dev/test-login)
- Redirect duplicate admin/dashboard.vue to /admin
- Update CLAUDE.md design system docs

server/api/admin/members/invite.post.js

@@ -56,7 +56,7 @@ export default defineEventHandler(async (event) => {
         .replace(/\n/g, '<br>')
         .replace(/\{loginLink\}/g, loginButton)
 
-      const { error: sendError } = await resend.emails.send({
+      const { error: emailError } = await resend.emails.send({
         from: 'Ghost Guild <welcome@babyghosts.org>',
         to: [member.email],
         subject: 'You\'re invited to Ghost Guild',
@@ -64,8 +64,8 @@ export default defineEventHandler(async (event) => {
         html: emailHtml
       })
 
-      if (sendError) {
-        results.push({ memberId: member._id, email: member.email, success: false, error: sendError.message })
+      if (emailError) {
+        results.push({ memberId: member._id, email: member.email, success: false, error: emailError.message })
         continue
       }