feat(materials): add campaign materials overlay for sessions

Let GMs manage and show images over the scene from the editor and control panel, with zoom tools, help docs, and full ru/en i18n.

Co-authored-by: Cursor <cursoragent@cursor.com>

app/renderer/editor/fileDrop.ts

@@ -3,6 +3,7 @@ import { useCallback, useEffect, useRef, useState, type DragEvent } from 'react'
 import { getDndApi } from '../shared/dndApi';
 
 const AUDIO_EXTENSIONS = new Set(['.mp3', '.wav', '.ogg', '.m4a', '.aac']);
+const MATERIAL_IMAGE_EXTENSIONS = new Set(['.png', '.jpg', '.jpeg', '.webp']);
 const PREVIEW_EXTENSIONS = new Set([
   '.png',
   '.jpg',
@@ -46,6 +47,17 @@ export function filterAudioFilePaths(paths: string[]): string[] {
   return paths.filter((path) => AUDIO_EXTENSIONS.has(fileExtension(path)));
 }
 
+export function filterMaterialImagePaths(paths: string[]): string[] {
+  return paths.filter((path) => MATERIAL_IMAGE_EXTENSIONS.has(fileExtension(path)));
+}
+
+export function pickFirstMaterialImagePath(paths: string[]): string | null {
+  for (const path of paths) {
+    if (MATERIAL_IMAGE_EXTENSIONS.has(fileExtension(path))) return path;
+  }
+  return null;
+}
+
 export function pickFirstPreviewFilePath(paths: string[]): string | null {
   for (const path of paths) {
     if (PREVIEW_EXTENSIONS.has(fileExtension(path))) return path;