CSI c Device Attributes Report returns 4 to indicate sixel support

"VT100 with GPO (Graphics Processor Option)"

Author: benjajaja

internal/app/darktile/termutil/csi.go

@@ -304,10 +304,14 @@ func (t *Terminal) csiWindowManipulation(params []string) (renderRequired bool)
 // Send Device Attributes (Primary/Secondary/Tertiary DA)
 func (t *Terminal) csiSendDeviceAttributesHandler(params []string) (renderRequired bool) {
 
-	// we are VT100
-	// for DA1 we'll respond ?1;2
+	// We are VT100 with:
+	// 1: STP (Selective Erase)
+	// 2: AVO (Advanced Video Option)
+	// 3: both STP and AVO
+	// 4: GPO (Graphics Processor Option (sixel))
+	// for DA1 we'll respond ?1;2;3;4
 	// for DA2 we'll respond >0;0;0
-	response := "?1;2"
+	response := "?1;2;4"
 	if len(params) > 0 && len(params[0]) > 0 && params[0][0] == '>' {
 		response = ">0;0;0"
 	}