perf(admin): cache global admin list totals via redisCache

Introduce getCachedAdminCount to cache un-filtered table count(*) queries in Redis for admin lists (starting with UsersPage), avoiding heavy full table scans on every request while keeping exact counts for search/filtered queries.

src/lib/services/admin-stats.ts

@@ -0,0 +1,26 @@
+import { count, type SQL } from "drizzle-orm";
+import type { MySqlTable } from "drizzle-orm/mysql-core";
+import { db } from "@/lib/db";
+import { redisCache } from "@/lib/redis-cache";
+
+/**
+ * Caches admin list totals when no filters are applied (no 'where' clause),
+ * preventing heavy COUNT(*) table scans on every request for large tables.
+ * Filtered queries bypass cache to ensure exact search result counts.
+ */
+export async function getCachedAdminCount(
+	table: MySqlTable,
+	cacheKey: string,
+	where?: SQL | undefined,
+): Promise<number> {
+	// Only cache the global count (where = undefined)
+	if (where) {
+		const [row] = await db.select({ total: count() }).from(table).where(where);
+		return Number(row?.total ?? 0);
+	}
+
+	return await redisCache(`admin:count:${cacheKey}`, 60, async () => {
+		const [row] = await db.select({ total: count() }).from(table);
+		return Number(row?.total ?? 0);
+	});
+}