fix(playground): increase Nginx burst from 20 to 50 (DAK-6961) (#229)

autoSeedDemoData consumes burst tokens on page load; if user visits
multiple lazy-seeded modes before Compare, burst is exhausted and
seedCmp gets 429s. Raising to 50 gives enough headroom for all modes.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: ferhimedamine

docker/nginx-playground.conf

@@ -2,7 +2,7 @@
 # Nginx — Dakera Playground Rate Limiting + TLS (DAK-6706)
 # =============================================================================
 # Rate zones:
-#   playground_api    10 req/min per IP, burst 20 — coarse DDoS ceiling (DAK-6710 AC8)
+#   playground_api    10 req/min per IP, burst 50 — coarse DDoS ceiling (DAK-6710/6961)
 #   playground_health 60 req/s per IP, burst 20 — /health (monitoring)
 #   playground_conn   20 concurrent connections per IP
 #
@@ -72,7 +72,7 @@ server {
     # server-side root-key injection (DAK-6713). The proxy forwards to the
     # engine on :3000.
     location / {
-        limit_req        zone=playground_api burst=20 nodelay;
+        limit_req        zone=playground_api burst=50 nodelay;
         limit_req_status 429;
 
         proxy_pass            http://127.0.0.1:3100;