Left-align menu entries, add a Dropdown field, scrollable and searchable menus

Menu entries are left-aligned and live in a ScrollContainer capped at 320 px, so a
long list (the parent picker holds every object of the scene) scrolls instead of
running off the screen. `Menu(items, { searchable: true })` puts a filter box above
the scroll area; Enter takes the first match. Filtering forces a relayout because
two queries with the same hit count leave the height unchanged, which would keep
the stale row positions.

Fields that open a menu are a new `Dropdown` widget: the value sits flush left and
the chevron is drawn flush right instead of being written into the label. A menu
opened below a field is never narrower than that field.

New debug hooks `overlayTexts()` / `overlayRect()` make the popup contents
assertable; e2e step 11 covers the cap, the scrolling and the search box.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/editor/debugHook.ts

@@ -1,4 +1,5 @@
 import { type Application, type Container, Text } from 'pixi.js';
+import { ui, Widget } from '../ui';
 import type { Editor } from './Editor';
 import type { EditorState } from './state';
 
@@ -32,9 +33,36 @@ export function installDebugHook(app: Application, state: EditorState, editor: E
     const p = node.getGlobalPosition();
     return { x: p.x + node.width / 2, y: p.y + node.height / 2 };
   };
+  /**
+   * The visible text of the overlay layer, in drawing order – everything an open popup shows.
+   * Menus hide filtered-out entries, so this is also what a search box currently leaves.
+   */
+  const overlayTexts = (): string[] => {
+    const out: string[] = [];
+    const walk = (node: Container): void => {
+      if (!node.visible) return;
+      if (node instanceof Text) {
+        if (node.text) out.push(node.text);
+        return;
+      }
+      for (const child of node.children) walk(child);
+    };
+    walk(ui().overlay);
+    return out;
+  };
+  /** Screen rectangle of the open popup (the backdrop is not a widget), or null when none is. */
+  const overlayRect = (): { x: number; y: number; w: number; h: number } | null => {
+    const popups = ui().overlay.children.filter((node): node is Widget => node instanceof Widget);
+    const popup = popups[popups.length - 1];
+    if (!popup) return null;
+    const p = popup.getGlobalPosition();
+    return { x: p.x, y: p.y, w: popup.w, h: popup.h };
+  };
   (window as unknown as { __gm: unknown }).__gm = {
     state,
     locate,
+    overlayTexts,
+    overlayRect,
     viewportCenter: () => centreOf(viewport),
     viewportInfo: () => viewport.debugInfo(),
     gameInfo: () => gameView.debugInfo(),