#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/scripting-parity.md

@@ -19,7 +19,7 @@ our own scripts; no real-world script library has been run against both apps.
 | Expression editing | Inline field, error bar, pick whip, Expression Language menu, external editors | Inline field that grows, error bar, pick whips (property and value), language menu | partial | External editor support (#364) |
 | Expression performance | Cached, multi-frame | Per-thread boa contexts | unknown | No benchmark |
 | Scripting object model | `app`, `Project`, items, layers, properties, keys, eases, render queue, `TextDocument`, `Shape`, markers, `File`/`Folder`, `Socket`, `app.settings` | Same classes, edits run through undoable engine commands; match names table | good | `crates/script` tests (≈ 10 test files) |
-| ScriptUI | Dialogs, palettes, dockable panels, resource strings, `onDraw` / ScriptUIGraphics | Same, dockable panels reopen at launch | good | `ui_scriptui`, `tests_ui*` |
+| ScriptUI | Dialogs, palettes, dockable panels, resource strings, `onDraw` / ScriptUIGraphics, mouse events | Same, dockable panels reopen at launch | good | `ui_scriptui`, `tests_ui*` |
 | Scripts menu, ScriptUI Panels folder | yes | yes | same | [plugins.md](plugins.md) |
 | Startup / Shutdown folders | yes | not run | missing | plugins.md |
 | `#include`, `#target` directives | yes | a script starting with one doesn't parse | missing | plugins.md; common in real scripts |