feat: RouterAI as 3rd image fallback via /responses + image_generation

- app_settings: ROUTERAI_BASE_URL, ROUTERAI_API_KEY, ROUTERAI_IMAGE_MODEL
- config/index.js: routeraiBaseUrl, routeraiApiKey, routeraiImageModel
- covers.js: generateCoverViaRouterAI() через /responses endpoint
  Цепочка: aiguoguo → Nyxos → RouterAI → local SVG

src/services/covers.js

@@ -270,6 +270,35 @@ async function generateCoverViaImagesEndpoint({ prompt }) {
  * Основной путь — /images/generations (aiguoguo199.com или любой OpenAI-совместимый).
  * Более стабильный чем /responses, поддерживает gpt-image-1-mini/gpt-image-2.
  */
+/**
+ * RouterAI — стабильный провайдер через /responses + image_generation tool.
+ * Используется как третий fallback когда aiguoguo и Nyxos недоступны.
+ */
+async function generateCoverViaRouterAI({ prompt }) {
+  const base  = config.ai.routeraiBaseUrl;
+  const key   = config.ai.routeraiApiKey;
+  const model = config.ai.routeraiImageModel || 'openai/gpt-5-image-mini';
+  const started = Date.now();
+  try {
+    const res = await axios.post(`${base}/responses`, {
+      model,
+      input: `Use the image_generation tool to create this illustration. Only call the tool, no text.\n\n${prompt.slice(0, 3000)}`,
+      tools: [{ type: 'image_generation' }],
+      tool_choice: { type: 'image_generation' },
+    }, {
+      headers: { Authorization: `Bearer ${key}` },
+      timeout: 120_000,
+    });
+    const imgCall = (res.data?.output || []).find(o => o.type === 'image_generation_call');
+    if (!imgCall?.result) throw new Error('No image in RouterAI response');
+    aiUsage.log({ provider: 'routerai', requestType: 'image_via_responses', model, imageCount: 1, durationMs: Date.now()-started, succeeded: true }).catch(() => {});
+    return { bytes: Buffer.from(imgCall.result, 'base64'), format: imgCall.output_format || 'png' };
+  } catch (err) {
+    aiUsage.log({ provider: 'routerai', requestType: 'image_via_responses', model, imageCount: 1, durationMs: Date.now()-started, succeeded: false, errorMessage: (err.response?.data?.error?.message || err.message || '').slice(0,500) }).catch(() => {});
+    throw err;
+  }
+}
+
 async function generateCoverViaImageGenerations({ prompt }) {
   const model = config.ai.imageModel || 'gpt-image-2';
 
@@ -302,8 +331,17 @@ async function generateCoverViaImageGenerations({ prompt }) {
   } catch (err) {
     const status = err.response?.status;
     if (!status || status >= 500) {
-      console.warn(`[Cover] primary failed (${status||'timeout'}), trying fallback aiguoguo...`);
-      return await tryProvider(config.ai.imageFallbackBaseUrl, config.ai.imageFallbackApiKey);
+      console.warn(`[Cover] primary failed (${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;
+      }
     }
     throw err;
   }