Add optional round-target billboard display

README.md

@@ -25,7 +25,7 @@ slightly faster round. Last player standing wins.
 All admin/config commands live under `/blockparty` (alias `/bp`) and work from console
 where it makes sense (`create`, `delete`, `enable`, `disable`, `info`, `list`, `reload`).
 Commands that require a physical location (`setlobby`, `setspawn`, `setspectator`,
-`pos1`, `pos2`) require a player sender.
+`setbillboard`, `pos1`, `pos2`) require a player sender.
 
 ### Admin
 | Command | Description |
@@ -38,6 +38,8 @@ Commands that require a physical location (`setlobby`, `setspawn`, `setspectator
 | `/blockparty setlobby <arena>` | Set the waiting-room location |
 | `/blockparty setspawn <arena>` | Set the in-game spawn location |
 | `/blockparty setspectator <arena>` | Set the spectator/eliminated location |
+| `/blockparty setbillboard <arena>` | (Optional) place a display block here that mirrors the current target color |
+| `/blockparty delbillboard <arena>` | Remove the billboard, if one is set |
 | `/blockparty pos1 <arena>` | Set floor region corner 1 |
 | `/blockparty pos2 <arena>` | Set floor region corner 2 |
 | `/blockparty setfloor <arena> <mat1,mat2,...>` | Set the allowed floor materials |
@@ -83,9 +85,12 @@ Commands that require a physical location (`setlobby`, `setspawn`, `setspectator
      still required once so BlockParty captures/serializes the exact layout it should restore
      each round (BlockParty does not scan the world every round — it restores from the saved
      layout for performance and determinism).
-8. `/bp info lobby1` to confirm there are no validation errors.
-9. `/bp enable lobby1`.
-10. Players run `/bp join lobby1`. Once `min-players` is reached the countdown starts
+8. Optionally, stand somewhere visible near/above the floor and run `/bp setbillboard lobby1`
+   to place a big display block that mirrors the round's target color — purely cosmetic and
+   entirely optional (see "Billboard" below).
+9. `/bp info lobby1` to confirm there are no validation errors.
+10. `/bp enable lobby1`.
+11. Players run `/bp join lobby1`. Once `min-players` is reached the countdown starts
     automatically; joining an arena mid-countdown is allowed by default
     (`allow-join-while-waiting: true`).
 
@@ -99,6 +104,23 @@ Commands that require a physical location (`setlobby`, `setspawn`, `setspectator
   (`generated-layout`) so it can be restored exactly, every round, without re-scanning or
   re-randomizing the world.
 
+### Billboard
+
+An arena billboard is a `BlockDisplay` entity that visually shows the currently selected
+target color/block each round, in addition to the title/actionbar/hotbar-item cues. It is
+entirely optional:
+
+- Per-arena: only spawned if `/bp setbillboard <arena>` has been run (stored as `billboard`
+  in the arena's yml). `/bp delbillboard <arena>` removes it.
+- Per-arena toggle: `billboard-enabled` in the arena's yml (default `true`) lets you keep the
+  location set but temporarily turn it off without deleting it.
+- Global toggle: `ui.billboard` in `config.yml` (default `true`) disables billboards across
+  every arena at once, e.g. for performance-constrained servers.
+
+The entity is non-persistent (not saved to the world, so it never survives a server restart on
+its own — BlockParty re-creates it on demand) and is despawned automatically when the arena is
+disabled, deleted, or the plugin shuts down, so it never leaks entities.
+
 ## Player usage
 
 - `/bp join <arena>` to enter the waiting lobby. Your inventory, armor, offhand, health,