feat: F4.8c the documentation mode's image export, as Java's

ExportRun measures Java's print panel (GUIContainer.prepareExportPanel) and
image on four projects and an empty one: 10 to spare around, a light grey
footer 20 below the lowest element, 20 below it, a transparent background,
the documentation painted as in the design. The sidebar gains Java's
"Exportieren": the surface painted with Canvas 2D (an SVG with a
foreignObject taints the canvas in WebKit) and saved under the project's
name; Java's message when saving fails. Not adopted: Java's empty image of
an empty project (its footer overflows). The editor takes a projectName;
the capture export shares the download helper.

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

packages/editor/test/i18n.test.ts

@@ -256,6 +256,8 @@ const FROM_JAVA: Readonly<Record<string, string>> = {
   'docu.styleItalic': 'guievents_msg20',
   'docu.styleBold': 'guievents_msg21',
   'docu.color': 'guievents_msg13',
+  'docu.export': 'docusidebar_msg5',
+  'docu.exportHint': 'docusidebar_msg6',
   'capture.title': 'lauscherdialog_msg1',
   'capture.number': 'rp_lauscher_msg1',
   'capture.time': 'rp_lauscher_msg2',
@@ -361,6 +363,8 @@ const FROM_JAVA: Readonly<Record<string, string>> = {
 
 /** Java's words, mended: the prompt says "Vermittlungsrechnerns" (guicontainer_msg1). */
 const FROM_JAVA_MENDED: Readonly<Record<string, readonly [string, (java: string) => string]>> = {
+  // Java's English misspells it.
+  'docu.saveFailed': ['guimainmemu_msg11', (java) => java.replace('occured', 'occurred')],
   'router.prompt': ['guicontainer_msg1', (java) => java.replace(' \\n ', ' ').replace('Vermittlungsrechnerns', 'Vermittlungsrechners')],
   // A label above its list, without the colon of Java's label beside it.
   'sheet.network': ['jhostkonfiguration_msg15', (java) => java.replace(/:$/, '')],