Fix cursor positioning and add utf8 import

internal/editor/state.go

@@ -3,6 +3,7 @@ package editor
 import (
 	"log"
 	"sort"
+	"unicode/utf8"
 
 	"pad/internal/browser"
 	"pad/internal/ui"
@@ -485,13 +486,10 @@ func SetCursorFromPoint(x, y float64) {
 
 	// 3. Check if tap is to the right of the last character on this line
 	if rightmostIdx != -1 && x > rightmostX {
-		// If rightmostIdx is the last glyph of the entire document
-		if rightmostIdx == len(layout.X)-1 {
-			TheState.Editor.CursorPosition = len(TheState.Editor.Buffer)
-		} else {
 		// Position after the last character on this line
-			TheState.Editor.CursorPosition = layout.ByteOffsets[rightmostIdx+1]
-		}
+		start := layout.ByteOffsets[rightmostIdx]
+		_, size := utf8.DecodeRuneInString(TheState.Editor.Buffer[start:])
+		TheState.Editor.CursorPosition = start + size
 		return
 	}