#766: deliver ScriptUI mouse events to script listeners

Problem: ScriptUI controls never sent mouse events to scripts.
addEventListener("mousedown" | "mouseup" | "mousemove" | "mouseover" |
"mouseout" | "click") listeners never ran, so custom-drawn controls
(onDraw + mouse, as DuScriptUI builds them) could not react to the pointer.
docs/plugins.md listed this as missing.

Fix: scriptui.js builds a ScriptUI MouseEvent (clientX/clientY relative to
the target, button, detail = click count, screenX/Y, modifier keys,
getModifierState, stopPropagation, preventDefault) and delivers it in the
capture, target and bubble phases. addEventListener takes the capture flag.
The parent walk is bounded, so a script-made parent cycle cannot hang it.
Each published control lists the mouse events a listener wants
(Widget::mouse, inherited from containers). The new scriptui.mouse
command dispatches one event with clamped, finite values and rejects
unknown types and disabled controls. The egui ScriptUI view hit-tests the
pointer over script windows and docked panels, skipping covered layers and
windows blocked by a modal dialog. It sends mouseover/mouseout,
mousemove, mousedown/mouseup with click counts, and a click carrying the
pointer details in place of the plain click, so a checkbox still toggles
once. Handlers run under the existing script limits; a throwing listener
reports an error and the window keeps working.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

docs/plugins.md

@@ -84,9 +84,12 @@ Supported controls: `panel`, `group`, `button`, `iconbutton`, `statictext`, `edi
 `tabbedpanel` / `tab` and `image`, with ScriptUI's automatic layout (`orientation`,
 `alignChildren`, `alignment`, `margins`, `spacing`, `preferredSize`), resource strings, event
 handlers (`onClick`, `onChange`, `onChanging`, `onClose`, `addEventListener`) and `onDraw` with
-ScriptUIGraphics. Mouse events (`mousedown`, `mousemove`…) aren't sent to scripts yet. Agents use
-a panel like a user: `scriptui.list`, `scriptui.get` (its controls), `scriptui.click`,
-`scriptui.set` and `scriptui.close`; every control has the automation id
+ScriptUIGraphics. Mouse events (`addEventListener("mousedown" | "mouseup" | "mousemove" |
+"mouseover" | "mouseout" | "click", handler, capture?)`) reach the control under the pointer and
+its containers (capture, target, bubble; `stopPropagation()`), with a MouseEvent carrying
+`clientX`/`clientY` relative to the target, `button`, `detail` (click count) and the modifier
+keys. Agents use a panel like a user: `scriptui.list`, `scriptui.get` (its controls),
+`scriptui.click`, `scriptui.set`, `scriptui.mouse` and `scriptui.close`; every control has the automation id
 `scriptui.<window>.<control id or name>`. The bundled sample `Layer Tools.jsx`
 (`crates/engine/scripts/ScriptUI Panels/`) and the Ease Presets extension below are longer
 examples.