feat(ui): avatar crop modal, health endpoint, leaner Dockerfile

- Add AvatarCropModal.svelte using cropperjs v1: 1:1 crop, 400×400 output,
  JPEG/WebP output, dark glassmorphic UI
- Rewrite profile page avatar upload to use presigned PUT flow (POST→PUT→PATCH)
  instead of sending raw FormData directly; crop modal opens on file select
- Add GET /health → {status:ok} for Docker healthcheck
- Simplify Dockerfile: drop runtime npm ci (adapter-node bundles all deps)
- Fix docker-compose UI healthcheck: /health route, 127.0.0.1 to avoid
  IPv6 localhost resolution failure in alpine busybox wget

docker-compose.yml

@@ -149,7 +149,7 @@ services:
     ports:
       - "${UI_PORT:-5252}:3000"
     healthcheck:
-      test: ["CMD", "wget", "-qO-", "http://localhost:3000/"]
+      test: ["CMD", "wget", "-qO-", "http://127.0.0.1:3000/health"]
       interval: 15s
       timeout: 5s
       retries: 3