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.

pixel/font_test.go

@@ -193,7 +193,7 @@ func hanging(punct func(rune) bool) func(rune) bool {
 }
 
 func TestMicroFont(t *testing.T) {
-	set := "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ+-.:/%! "
+	set := "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ+-#.:/%! "
 	seen := map[[MicroHeight]uint8]rune{}
 	for _, r := range set {
 		g := microGlyph(r)
@@ -213,8 +213,8 @@ func TestMicroFont(t *testing.T) {
 	}
 	defer func() {
 		if recover() == nil {
-			t.Fatal("micro '#' did not panic")
+			t.Fatal("micro '@' did not panic")
 		}
 	}()
-	MicroWidth("#")
+	MicroWidth("@")
 }