feat(ui): ui_scale and ui_box, on-submit, zoom (and a length over a length in calc), on-hold

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/ludic.ui/hold.ludic

@@ -0,0 +1,28 @@
+# hold.ludic - on-hold: every frame a control is held down - by the pointer (wherever it goes until it
+# is let go), or by Enter or the pad's A on the focus - with event.dt, the seconds since the last
+# frame, and event.t, how long it has been held, on the ui clock
+var hd_key: string = ""
+var hd_t0: float = 0.0
+var hd_last: float = 0.0
+function hd_tick(root: UiNode) -> void {
+  var key = fr_key_press
+  if fr_press_key != "" and in_now.down { key = fr_press_key }
+  if key == "" {
+    hd_key = ""
+    return
+  }
+  let now = an_now()
+  if key != hd_key {
+    hd_key = key
+    hd_t0 = now
+    hd_last = now
+  }
+  let n = fr_node(root, key)
+  if n != null {
+    let v = Value.object()
+    Value.put(v, "dt", Value.float(now - hd_last))
+    Value.put(v, "t", Value.float(now - hd_t0))
+    ui_fire(n, "hold", v)
+  }
+  hd_last = now
+}