plasma: ESC P bitmap rows through the feedback endpoint (plasma row)

PlasmaCommands.GraphicsWrite/GraphicsRow port the display firmware graphics
command (ESC P s y x w h, MSB-left); PlasmaDisplay.RowAsync writes a locked
whole-row update; the line protocol gains `plasma row <y> <hex32>`. The
router plasma slot becomes a bounded FIFO queue: rows stream in order (a
frame must not tear), texts still coalesce to the newest, clear flushes, cap
128 with counted drops. Docs updated; 442 tests.

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

tests/RioJoy.Core.Tests/Feedback/FeedbackLineParserTests.cs

@@ -184,6 +184,41 @@ public class FeedbackLineParserTests
     {
         Assert.NotEmpty(ParseError(line));
     }
+
+    [Fact]
+    public void PlasmaRow_ParsesRowAndHexData()
+    {
+        FeedbackCommand cmd = Parse("plasma row 5 80000000000000000000000000000001");
+        Assert.Equal(FeedbackCommandKind.PlasmaRow, cmd.Kind);
+        Assert.Equal(5, cmd.Y);
+        Assert.NotNull(cmd.Data);
+        Assert.Equal(16, cmd.Data!.Length);
+        Assert.Equal(0x80, cmd.Data[0]); // leftmost pixel lit (MSB-first)
+        Assert.Equal(0x01, cmd.Data[15]);
+        Assert.All(cmd.Data.Skip(1).Take(14), b => Assert.Equal(0, b));
+    }
+
+    [Fact]
+    public void PlasmaRow_HexRowNumber_AndMixedCaseHex()
+    {
+        FeedbackCommand cmd = Parse("PLASMA ROW 0x1F AaBbCcDdEeFf00112233445566778899");
+        Assert.Equal(31, cmd.Y);
+        Assert.Equal(0xAA, cmd.Data![0]);
+        Assert.Equal(0x99, cmd.Data[15]);
+    }
+
+    [Theory]
+    [InlineData("plasma row")]                                        // no row
+    [InlineData("plasma row 5")]                                      // no data
+    [InlineData("plasma row 32 80000000000000000000000000000001")]    // row out of range
+    [InlineData("plasma row 5 8000")]                                 // too short
+    [InlineData("plasma row 5 800000000000000000000000000000010A")]   // too long
+    [InlineData("plasma row 5 8000000000000000000000000000000G")]     // non-hex char
+    [InlineData("plasma row 5 80000000000000000000000000000001 x")]   // trailing token
+    public void PlasmaRow_Malformed_ReturnsErrorText(string line)
+    {
+        Assert.NotEmpty(ParseError(line));
+    }
 }
 
 public class FeedbackLineBufferTests