feat: F4.6f3 the file explorer and the image viewer

Oracle FileExplorerWindowRun uses Java's explorer and viewer windows as a
person does (the right-click menu, Java's questions answered, the import
window, the viewer's open). Both windows work on the document's files
through the core's operations: the tree of folders and files, the chosen
folder's entries, Java's menu (also as buttons, no right click needed),
copy that stays and cut that goes once pasted, the import; the viewer's
picture and title. Not taken from Java: a file chosen in the tree taken
for a folder, pictures laid over each other, a text file as an empty
picture. writeFiles numbers the entries in the file system's order again
when a rename made a new key.

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

packages/core/src/runtime/apps/filePrograms.ts

@@ -20,7 +20,8 @@
 //   is refused (Java makes such a file), a name with "/" leads into a
 //   folder (Java makes a file whose name holds the separator);
 // - "open" opens text files only (Java shows an image as its Base64 text)
-//   and keeps the open file when it finds none (Java forgets it);
+//   and keeps the open file when it finds none (Java forgets it); the image
+//   viewer's opens images only (Java shows another file as an empty picture);
 // - a text file's size is its length in characters (as the command line's).
 
 import type { VirtualFileContent, VirtualFileSystem } from '../../model/virtualFileSystem.js';
@@ -259,6 +260,19 @@ export function openText(files: VirtualFileSystem, folder: string, name: string)
   return entry.content.kind === 'text' ? { path: entry.path, text: entry.content.text } : 'notText';
 }
 
+/**
+ * The image viewer's "open" (holeDatei of the dialog's folder and name, as
+ * the editor's): an image file's path, bytes and media type. Java shows any
+ * file it finds — another as an empty picture —, and with none keeps what it
+ * shows; here a file that is not an image is notImage, none notFound.
+ */
+export function openImage(files: VirtualFileSystem, folder: string, name: string): { readonly path: string; readonly data: Uint8Array; readonly mediaType: string } | 'notFound' | 'notImage' {
+  // No name is the folder itself: not found.
+  const entry = found(files, evaluatedPath(name.startsWith('/') ? name : `${folder}/${name}`));
+  if (entry === undefined || entry.content.kind === 'directory') return 'notFound';
+  return entry.content.kind === 'image' ? { path: entry.path, data: entry.content.data, mediaType: entry.content.mediaType } : 'notImage';
+}
+
 /** The image viewer's "open": an image file's bytes and media type; none for any other file. */
 export function imageFile(files: VirtualFileSystem, path: string): { readonly data: Uint8Array; readonly mediaType: string } | undefined {
   const entry = found(files, path);