test: import 38 channelserver test files from v9.2.x-stable

Port test files from v9.2.x-stable branch to increase channelserver
coverage from 13.8% to 25.6% (556 tests passing).

Adapted all files to main's struct definitions: config import alias,
Airou/CatDefinition rename, packet field mismatches, Raviente struct
differences, and maxPlayers defaults. Removed tests referencing
production code not yet on main (Player, FestivalColour, etc.).
Excluded handlers_register_test.go (Raviente completely redesigned).

server/channelserver/handlers_mutex_test.go

@@ -0,0 +1,77 @@
+package channelserver
+
+import (
+	"testing"
+)
+
+// Test that all mutex handlers don't panic (they are empty implementations)
+
+func TestHandleMsgSysCreateMutex(t *testing.T) {
+	server := createMockServer()
+	session := createMockSession(1, server)
+
+	// Should not panic (empty handler)
+	defer func() {
+		if r := recover(); r != nil {
+			t.Errorf("handleMsgSysCreateMutex panicked: %v", r)
+		}
+	}()
+
+	handleMsgSysCreateMutex(session, nil)
+}
+
+func TestHandleMsgSysCreateOpenMutex(t *testing.T) {
+	server := createMockServer()
+	session := createMockSession(1, server)
+
+	// Should not panic (empty handler)
+	defer func() {
+		if r := recover(); r != nil {
+			t.Errorf("handleMsgSysCreateOpenMutex panicked: %v", r)
+		}
+	}()
+
+	handleMsgSysCreateOpenMutex(session, nil)
+}
+
+func TestHandleMsgSysDeleteMutex(t *testing.T) {
+	server := createMockServer()
+	session := createMockSession(1, server)
+
+	// Should not panic (empty handler)
+	defer func() {
+		if r := recover(); r != nil {
+			t.Errorf("handleMsgSysDeleteMutex panicked: %v", r)
+		}
+	}()
+
+	handleMsgSysDeleteMutex(session, nil)
+}
+
+func TestHandleMsgSysOpenMutex(t *testing.T) {
+	server := createMockServer()
+	session := createMockSession(1, server)
+
+	// Should not panic (empty handler)
+	defer func() {
+		if r := recover(); r != nil {
+			t.Errorf("handleMsgSysOpenMutex panicked: %v", r)
+		}
+	}()
+
+	handleMsgSysOpenMutex(session, nil)
+}
+
+func TestHandleMsgSysCloseMutex(t *testing.T) {
+	server := createMockServer()
+	session := createMockSession(1, server)
+
+	// Should not panic (empty handler)
+	defer func() {
+		if r := recover(); r != nil {
+			t.Errorf("handleMsgSysCloseMutex panicked: %v", r)
+		}
+	}()
+
+	handleMsgSysCloseMutex(session, nil)
+}