fix: react-doctor no-barrel-import 20→1 (direct design-system imports)

Convert ./design-system barrel imports to direct file paths across
19 admin components. Remaining 1 (db/client.ts) is Drizzle schema
which legitimately requires namespace import for drizzle() helper.

src/components/admin/WaterLogAdminPanel.tsx

@@ -48,7 +48,7 @@ import {
   type WaterLogReportRow,
 } from "@/lib/water-log-reporting";
 import { WaterGauge, SeasonMark } from "@/components/water/icons";
-import { AdminButton } from "./design-system";
+import AdminButton from "./design-system/AdminButton";
 import { formatDate, formatDateTime } from "@/lib/format-date";
 
 type Props = {