feat: add annotation tool settings menus

internal/application/annotation_test.go

@@ -140,3 +140,34 @@ func TestApplyAnnotationsWithScaleDrawsTextAtDevicePosition(t *testing.T) {
 		t.Fatalf("expected text to be drawn near scaled x=100, min red x=%d", minX)
 	}
 }
+
+func TestApplyAnnotationsUsesStrokeWidth(t *testing.T) {
+	src := image.NewRGBA(image.Rect(0, 0, 80, 80))
+	draw.Draw(src, src.Bounds(), &image.Uniform{C: color.White}, image.Point{}, draw.Src)
+
+	var buf bytes.Buffer
+	if err := png.Encode(&buf, src); err != nil {
+		t.Fatalf("encode source: %v", err)
+	}
+
+	out, err := ApplyAnnotations(buf.Bytes(), []Annotation{
+		{
+			Tool:        "rect",
+			Color:       "#ef4444",
+			Points:      []Point{{X: 20, Y: 20}, {X: 60, Y: 60}},
+			StrokeWidth: 8,
+		},
+	}, 1)
+	if err != nil {
+		t.Fatalf("apply annotations: %v", err)
+	}
+
+	img, err := png.Decode(bytes.NewReader(out))
+	if err != nil {
+		t.Fatalf("decode output: %v", err)
+	}
+	got := color.RGBAModel.Convert(img.At(20, 24)).(color.RGBA)
+	if got.R < 180 || got.G > 180 || got.B > 180 {
+		t.Fatalf("expected thick rectangle stroke to cover y=24, got %#v", got)
+	}
+}