test: expand channelserver coverage from 16% to 20%

Add comprehensive tests for handler functions and utilities:
- Achievement system (GetAchData, curves, mappings)
- Language system (getLangStrings)
- Core handlers (empty handlers, simple responses)
- Cafe/boost handlers
- Diva defense handlers
- Reward, caravan, tactics handlers
- Festa/ranking handlers
- Cast binary constants

server/channelserver/handlers_cafe_test.go

@@ -0,0 +1,98 @@
+package channelserver
+
+import (
+	"testing"
+
+	"erupe-ce/network/mhfpacket"
+)
+
+func TestHandleMsgMhfGetBoostTime(t *testing.T) {
+	server := createMockServer()
+	session := createMockSession(1, server)
+
+	pkt := &mhfpacket.MsgMhfGetBoostTime{
+		AckHandle: 12345,
+	}
+
+	handleMsgMhfGetBoostTime(session, pkt)
+
+	select {
+	case p := <-session.sendPackets:
+		// Response should be empty bytes for this handler
+		if p.data == nil {
+			t.Error("Response packet data should not be nil")
+		}
+	default:
+		t.Error("No response packet queued")
+	}
+}
+
+func TestHandleMsgMhfPostBoostTimeQuestReturn(t *testing.T) {
+	server := createMockServer()
+	session := createMockSession(1, server)
+
+	pkt := &mhfpacket.MsgMhfPostBoostTimeQuestReturn{
+		AckHandle: 12345,
+	}
+
+	handleMsgMhfPostBoostTimeQuestReturn(session, pkt)
+
+	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 TestHandleMsgMhfPostBoostTime(t *testing.T) {
+	server := createMockServer()
+	session := createMockSession(1, server)
+
+	// Empty handler - should not panic
+	defer func() {
+		if r := recover(); r != nil {
+			t.Errorf("handleMsgMhfPostBoostTime panicked: %v", r)
+		}
+	}()
+
+	handleMsgMhfPostBoostTime(session, nil)
+}
+
+func TestHandleMsgMhfPostBoostTimeLimit(t *testing.T) {
+	server := createMockServer()
+	session := createMockSession(1, server)
+
+	// Empty handler - should not panic
+	defer func() {
+		if r := recover(); r != nil {
+			t.Errorf("handleMsgMhfPostBoostTimeLimit panicked: %v", r)
+		}
+	}()
+
+	handleMsgMhfPostBoostTimeLimit(session, nil)
+}
+
+func TestCafeBonusStruct(t *testing.T) {
+	// Test CafeBonus struct can be created
+	bonus := CafeBonus{
+		ID:       1,
+		TimeReq:  3600,
+		ItemType: 1,
+		ItemID:   100,
+		Quantity: 5,
+		Claimed:  false,
+	}
+
+	if bonus.ID != 1 {
+		t.Errorf("ID = %d, want 1", bonus.ID)
+	}
+	if bonus.TimeReq != 3600 {
+		t.Errorf("TimeReq = %d, want 3600", bonus.TimeReq)
+	}
+	if bonus.Claimed {
+		t.Error("Claimed should be false")
+	}
+}