plasma: hide the cursor before anything draws

The firmware parks a cursor artifact wherever text last ended, and nothing
ever turned it off - the native games did, once at startup (ESC G 0,
L4PLASMA.CPP), which is why the cabinet never showed it. Seen on the bench as
a stray block sitting in the Descent 3 nameplate.

ShowGreetingAsync now sends cursor-hidden as its first act on every plasma
open, before the clear and greeting, so every path that follows - greeting,
feedback text, bitmap rows - draws on a cursorless panel. PlasmaDisplay gains
the CursorAsync wrapper for the ESC G command the command builder already had.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/RioJoy.Core/Plasma/PlasmaDisplay.cs

@@ -25,6 +25,15 @@ public sealed class PlasmaDisplay
     public Task ClearAsync(CancellationToken ct = default) =>
         WriteLockedAsync(new[] { PlasmaCommands.Clear() }, ct);
 
+    /// <summary>
+    /// Set the cursor mode (<c>ESC G n</c>): 0 hidden, 1 steady, 3 flashing.
+    /// The native games send <c>ESC G 0</c> once at startup
+    /// (<c>L4PLASMA.CPP</c>) — without it the firmware's cursor artifact sits
+    /// wherever text last ended.
+    /// </summary>
+    public Task CursorAsync(byte mode, CancellationToken ct = default) =>
+        WriteLockedAsync(new[] { PlasmaCommands.Cursor(mode) }, ct);
+
     public Task CursorHomeAsync(CancellationToken ct = default) =>
         WriteLockedAsync(new[] { PlasmaCommands.CursorHome() }, ct);
 

src/RioJoy.Tray/RioCoordinator.cs

@@ -337,6 +337,11 @@ public sealed class RioCoordinator : IDisposable
     {
         try
         {
+            // Hide the cursor before anything draws, as the native games did
+            // once at startup (ESC G 0, L4PLASMA.CPP): the firmware otherwise
+            // leaves its cursor artifact wherever text last ended, which reads
+            // as a stray block parked in the nameplate.
+            await plasma.CursorAsync(0).ConfigureAwait(false);
             await plasma.ClearAsync().ConfigureAwait(false);
             if (!string.IsNullOrWhiteSpace(greeting))
                 await plasma.PosTextAsync(greeting!).ConfigureAwait(false); // (0,0) = auto-center