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/assets/css/main.css

@@ -29,6 +29,7 @@
   --text-faint: #8a7e6a;
   --parch: #2a2015;
   --parch-text: #ede4d0;
+  --parch-text-dim: #b8ae98;
   --c-community: #7a4838;
   --c-founder: #8a4420;
   --c-practitioner: #2a4650;
@@ -52,6 +53,7 @@
   --text-faint: #5a5040;
   --parch: #ede4d0;
   --parch-text: #2a2015;
+  --parch-text-dim: #5a5040;
   --c-community: #a06850;
   --c-founder: #c06030;
   --c-practitioner: #4a7080;