fix(api): batch member user lookups on guild load (#2783)

deploy/self-hosting/.env.example

@@ -365,8 +365,9 @@ FLUXER_DISCOVERY_ENABLED=true
 # messages, 320 for snowflakes and 64 elsewhere, and they govern every service
 # Compose does not forward this to. A router holds a slot for the whole round
 # trip to its shard, so this is a ceiling on requests in flight at once and not a
-# rate: too low a value does not slow requests down, it rejects them, and the api
-# turns that rejection into a 503.
+# rate: too low a value does not slow requests down, it rejects them. The api
+# turns that rejection into a 503 and logs "shard rejected the request because
+# it is at its concurrency limit".
 #FLUXER_SVC_MAX_CONCURRENT_REQUESTS=192
 
 # The api and the Rust services name their fixed Postgres statement shapes so the