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

app/pages/member/dashboard.vue

@@ -1,5 +1,6 @@
 <template>
   <div class="dashboard">
+    <ClientOnly>
     <!-- Loading State -->
     <div v-if="authPending" class="loading-state">
       <div class="spinner" />
@@ -149,6 +150,14 @@
         </div>
       </div>
     </template>
+
+    <template #fallback>
+      <div class="loading-state">
+        <div class="spinner" />
+        <p>Loading your dashboard...</p>
+      </div>
+    </template>
+    </ClientOnly>
   </div>
 </template>