refactor: rename Kopaya to Eryx

Rename the product, runtime surfaces, sidecar projects, docs, tests, and packaging outputs from Kopaya to Eryx across the repository.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

sidecar/tests/Eryx.AgentHost.Tests/StreamingTextMergerTests.cs

@@ -0,0 +1,39 @@
+using Eryx.AgentHost.Services;
+
+namespace Eryx.AgentHost.Tests;
+
+public sealed class StreamingTextMergerTests
+{
+    [Fact]
+    public void Merge_AppendsPlainDeltas()
+    {
+        Assert.Equal("I am going", StreamingTextMerger.Merge("I am", " going"));
+    }
+
+    [Fact]
+    public void Merge_ReplacesWithGrowingSnapshot()
+    {
+        Assert.Equal("I am going", StreamingTextMerger.Merge("I am", "I am going"));
+    }
+
+    [Fact]
+    public void Merge_PreservesCurrentTextForDuplicateSubset()
+    {
+        Assert.Equal("I am going", StreamingTextMerger.Merge("I am going", "going"));
+    }
+
+    [Fact]
+    public void Merge_UsesOverlapToAvoidDuplicateJoins()
+    {
+        Assert.Equal("Hello world", StreamingTextMerger.Merge("Hello wor", "world"));
+    }
+
+    [Fact]
+    public void Merge_ReplacesWithRevisedSnapshotWhenMostTokensOverlap()
+    {
+        const string current = "I mirror the existing button pattern and add brief toggle docs.";
+        const string incoming = "I found the standalone component pattern and I am updating toggle docs next.";
+
+        Assert.Equal(incoming, StreamingTextMerger.Merge(current, incoming));
+    }
+}