Add media components 346-365; input.SlideBase, guarded Pad

An audio player with transport, scrubber and volume; an equalizer and
a visualizer; a playlist; a cassette, cartridge and record that turn
while they play and hold where they stop; piano keys, a step sequencer
and a tracker you can type into; a waveform, a 16:9 video frame, an
image compare, a gallery, a filmstrip, a record button and an FM tuner.

input exports SlideBase, the undrawn rail its sliders share; the
gallery treats exported Bases as building blocks, not components.
pixel's micro font gains '#' for notes like C#4. pixel.Pad and the
slide rail read input only while their base is enabled, so Inert or a
fresh Disabled stops a drag or a key already sent. AGENTS records why
a drawn container keeps the DISABLED description: MyGo paints a
disabled subtree at half opacity.

media/imagecompare.go

@@ -0,0 +1,54 @@
+package media
+
+import (
+	"fmt"
+	"log/slog"
+	"math"
+
+	"github.com/egoist/mygo/ui"
+
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/input"
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/pixel"
+)
+
+type ImageCompareOptions struct {
+	// Scale is dots per picture dot, 1–4; zero means 2.
+	Scale    int
+	Disabled bool
+}
+
+type ImageCompareResult struct {
+	Element *ui.Element
+	Changed bool
+}
+
+// ImageCompare shows before left of *split, after right.
+func ImageCompare(c *ui.Context, text string, before, after *pixel.Sprite, split *float64, o ImageCompareOptions) ImageCompareResult {
+	k := pixel.K(c)
+	sameSize("ImageCompare", []*pixel.Sprite{before, after})
+	if !(*split >= 0 && *split <= 1) {
+		panic(fmt.Sprintf("media: ImageCompare split %v outside 0–1", *split))
+	}
+	s := scale("ImageCompare", o.Scale, 2)
+	w, h := before.W*s, before.H*s
+	shell, st, changed := input.SlideBase(c, text, split, input.RailOptions{Disabled: o.Disabled})
+	if changed {
+		slog.Debug("8bit: image compare", "label", text, "split", *split)
+	}
+	at := *split
+	shell.Size(k.D(w), k.D(h)).Draw(func(p *ui.Painter, r ui.Rect) {
+		g := k.Canvas(p, r)
+		x := int(math.Round(at * float64(w)))
+		g.Sprite(0, 0, before, 0, pixel.Ink, s)
+		g.Clip(x, 0, w-x, h, func() { g.Sprite(0, 0, after, 0, pixel.Ink, s) })
+		g.VLine(min(x, w-1), 0, h, pixel.Edge)
+		// The grip stays whole at either edge.
+		gx := max(0, min(w-7, x-3))
+		g.Frame(gx, h/2-5, 7, 11, pixel.Raised, pixel.Face)
+		for _, d := range []int{-2, 0, 2} {
+			g.HLine(gx+2, h/2+d, 3, pixel.Shade)
+		}
+		g.Finish(st)
+	})
+	return ImageCompareResult{Element: shell, Changed: changed}
+}