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_rengoku_test.go

@@ -0,0 +1,53 @@
+package channelserver
+
+import (
+	"testing"
+
+	"erupe-ce/network/mhfpacket"
+)
+
+func TestHandleMsgMhfGetRengokuRankingRank(t *testing.T) {
+	server := createMockServer()
+	session := createMockSession(1, server)
+
+	pkt := &mhfpacket.MsgMhfGetRengokuRankingRank{
+		AckHandle: 12345,
+	}
+
+	handleMsgMhfGetRengokuRankingRank(session, pkt)
+
+	// Verify response packet was queued
+	select {
+	case p := <-session.sendPackets:
+		if len(p.data) == 0 {
+			t.Error("Response packet should have data")
+		}
+	default:
+		t.Error("No response packet queued")
+	}
+}
+
+func TestRengokuScoreStruct(t *testing.T) {
+	score := RengokuScore{
+		Name:  "TestPlayer",
+		Score: 12345,
+	}
+
+	if score.Name != "TestPlayer" {
+		t.Errorf("Name = %s, want TestPlayer", score.Name)
+	}
+	if score.Score != 12345 {
+		t.Errorf("Score = %d, want 12345", score.Score)
+	}
+}
+
+func TestRengokuScoreStruct_DefaultValues(t *testing.T) {
+	score := RengokuScore{}
+
+	if score.Name != "" {
+		t.Errorf("Default Name should be empty, got %s", score.Name)
+	}
+	if score.Score != 0 {
+		t.Errorf("Default Score should be 0, got %d", score.Score)
+	}
+}