Ship production optimization M1-M12.5A: queues, metrics, HTTP observability, and vector search reliability.

Keep similar-ai from tripping the global circuit on a lone URL 502, clamp Qdrant search to 100, and add Server-Timing plus slow-request logging. Studio shared props, Academy S3 exists caching, heat chunking, and Redis/scheduler hygiene stay in this rollout.

deploy/nginx/skinbase-vhost-performance-log.snippet

@@ -0,0 +1,16 @@
+# M12 — add INSIDE the HTTPS server { } for skinbase.org, next to the
+# existing combined access_log. Keep the original line unchanged.
+#
+#     access_log /var/log/nginx/skinbase.org-access.log;
+#     access_log /var/log/nginx/skinbase-performance.log skinbase_perf;
+#
+# Locations that already set `access_log off;` (static assets, /photo/*.jpg)
+# remain excluded from both logs.
+# File is created as 0640 www-data adm by nginx; logrotate /var/log/nginx/*.log
+# already rotates it (daily, 14 copies).
+#
+# After install:
+#   sudo nginx -t && sudo systemctl reload nginx
+# Never `restart` nginx for this change.
+
+access_log /var/log/nginx/skinbase-performance.log skinbase_perf;