feat: image quality param — low for posts, medium for article covers

covers.js: generateCoverViaRouterAI принимает quality='medium' по умолчанию
postImages.js: quality='low' для постов TG/VK (₽0.25 vs ₽0.84)
Экономия 70% на генерации картинок к постам

src/services/postImages.js

@@ -94,7 +94,7 @@ Strictly: no text, no letters, no logos, no faces of real people.`;
       const res = await axios.post(`${config.ai.routeraiBaseUrl}/responses`, {
         model,
         input: `Use the image_generation tool to create this illustration. Only call the tool, no text.\n\n${prompt.slice(0, 3000)}`,
-        tools: [{ type: 'image_generation' }],
+        tools: [{ type: 'image_generation', quality: 'low' }],
         tool_choice: { type: 'image_generation' },
       }, { headers: { Authorization: `Bearer ${config.ai.routeraiApiKey}` }, timeout: 120_000 });
       const imgCall = (res.data?.output || []).find(o => o.type === 'image_generation_call');