feat(admin): rename series route and add tags review page

Rename /admin/series-management to /admin/series so it follows the
/admin/<section> convention; the breadcrumb's auto-derived parent link
is now a real route (was a dead /admin/series link).

Add an /admin/tags page to review pending TagSuggestions — list,
approve (creates the Tag), reject — backed by new admin endpoints and a
tagSuggestionReviewSchema. Resolves the dead /admin/tags alert link.

server/utils/schemas.js

@@ -388,6 +388,10 @@ export const adminTagCreateSchema = z.object({
   pool: z.enum(['craft', 'cooperative'])
 })
 
+export const tagSuggestionReviewSchema = z.object({
+  action: z.enum(['approve', 'reject'])
+})
+
 // --- Board post / channel schemas ---
 
 export const boardPostCreateSchema = z.object({