feat: speed up admin clone import and enable Cache Components

- Clone import: defer FurnitureData.json writes and append all entries in a
  single batched write instead of one read-modify-write per item, removing
  the main serialization bottleneck for large batches.
- Clone import: raise SSE batch concurrency cap from 5 to 10 and bump the
  clone client/route default from 2 to 6.
- Add a flush hook to runSseBatch so callers can batch deferred work before
  batch_complete is emitted, and surface flush errors as an error event.
- Enable Next.js Cache Components (instant: false opt-out) and silence the
  related build warnings in next.config.ts.
- Switch isomorphic-dompurify to dompurify and refresh dependencies.

src/app/api/health/route.ts

@@ -7,8 +7,6 @@ import { clientIp, rateLimit } from "@/lib/rate-limit";
 import { redis } from "@/lib/redis";
 import { rcon } from "@/lib/services/rcon";
 
-export const dynamic = "force-dynamic";
-
 /**
  * Ops health probe: database reachability, Redis (when configured), emulator
  * RCON, SMTP (when configured), and runtime info. Returns HTTP 200 always