Admin-UI: document erasure_coding strict_placement and free_slots_deadband

Admin-UI.md

@@ -166,6 +166,8 @@ min_size_mb = 30
 collection_filter = ""
 preferred_tags = ["fast", "ssd"]
 replica_placement = ""
+strict_placement = false
+free_slots_deadband = 0  # nodes within M free volume slots tie; fewer live shards wins
 ```
 
 Keys set in `admin.toml` are applied every time the admin server starts and override values saved from the admin UI; keys left out keep their saved or default values. This makes the settings survive data directory loss, such as a recreated PVC. Requires `-dataDir`.