feat: routerai as primary image provider, Nyxos as fallback

- covers.js: RouterAI /responses → Nyxos /images/generations → SVG
- postImages.js: RouterAI /responses → Nyxos /images/generations
- config: imageBaseUrl = routerai, imageFallbackBaseUrl = nyxos
- app_settings: AI_IMAGE_BASE_URL = routerai, MODEL = gpt-5-image-mini

src/services/covers.js

@@ -325,23 +325,14 @@ async function generateCoverViaImageGenerations({ prompt }) {
     }
   }
 
-  // Основной: Nyxos Plus
+  // Основной: RouterAI /responses (стабильный)
   try {
-    return await tryProvider(config.ai.imageBaseUrl, config.ai.imageApiKey);
+    return await generateCoverViaRouterAI({ prompt });
   } catch (err) {
     const status = err.response?.status;
     if (!status || status >= 500) {
-      console.warn(`[Cover] primary failed (${status||'timeout'}), trying Nyxos fallback...`);
-      try {
-        return await tryProvider(config.ai.imageFallbackBaseUrl, config.ai.imageFallbackApiKey);
-      } catch (err2) {
-        const status2 = err2.response?.status;
-        if ((!status2 || status2 >= 500) && config.ai.routeraiApiKey) {
-          console.warn(`[Cover] Nyxos failed (${status2||'timeout'}), trying RouterAI /responses...`);
-          return await generateCoverViaRouterAI({ prompt });
-        }
-        throw err2;
-      }
+      console.warn(`[Cover] RouterAI failed (${status||'timeout'}), trying Nyxos fallback...`);
+      return await tryProvider(config.ai.imageFallbackBaseUrl, config.ai.imageFallbackApiKey);
     }
     throw err;
   }