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/my-updates.vue

@@ -10,6 +10,7 @@
 
       <!-- Main Content -->
       <div class="content-main">
+        <ClientOnly>
 
         <!-- Stats + New Update row -->
         <div v-if="isAuthenticated && !pending" class="stats-row">
@@ -108,6 +109,14 @@
           <NuxtLink to="/updates/new" class="btn btn-primary">+ Post Your First Update</NuxtLink>
         </div>
 
+        <template #fallback>
+          <div class="state-box">
+            <div class="spinner"></div>
+            <p class="state-text">Loading your updates...</p>
+          </div>
+        </template>
+        </ClientOnly>
+
       </div>
 
       <!-- Events Mini Sidebar -->