refactor(channelserver): consolidate tests into matching source test files

Move ~300 test functions from 21 catch-all files (handlers_core_test.go,
handlers_coverage*_test.go, *_coverage_test.go) into the *_test.go file
matching each handler's source file. This makes tests discoverable by
convention: tests for handlers_guild.go live in handlers_guild_test.go.

New files: handlers_guild_mission_test.go, sys_time_test.go.
No test logic changed — pure file reorganization.

server/channelserver/handlers_quest_test.go

@@ -782,3 +782,36 @@ func TestHandleMsgSysGetFile_ExistingQuestFile(t *testing.T) {
 		t.Errorf("expected success ack (ErrorCode=0) for existing quest file, got ErrorCode=%d", errorCode)
 	}
 }
+
+func TestHandleMsgMhfLoadFavoriteQuest(t *testing.T) {
+	server := createMockServer()
+	server.charRepo = newMockCharacterRepo()
+	session := createMockSession(100, server)
+
+	pkt := &mhfpacket.MsgMhfLoadFavoriteQuest{AckHandle: 1}
+	handleMsgMhfLoadFavoriteQuest(session, pkt)
+
+	select {
+	case <-session.sendPackets:
+	default:
+		t.Error("expected response")
+	}
+}
+
+func TestHandleMsgMhfSaveFavoriteQuest(t *testing.T) {
+	server := createMockServer()
+	server.charRepo = newMockCharacterRepo()
+	session := createMockSession(100, server)
+
+	pkt := &mhfpacket.MsgMhfSaveFavoriteQuest{
+		AckHandle: 1,
+		Data:      []byte{0x01, 0x00, 0x01, 0x00, 0x01},
+	}
+	handleMsgMhfSaveFavoriteQuest(session, pkt)
+
+	select {
+	case <-session.sendPackets:
+	default:
+		t.Error("expected response")
+	}
+}