feat: image rubrics with AI selection for cover variety

- channel_style.image_rubrics (JSONB): 6 рубрик для ZeroPost-блога
  (tech-photo, 3d-device, code-screen, data-flow, ai-neural, cinematic-tech)
- selectRubric(): haiku выбирает рубрику по заголовку+тегам статьи
- generateCover(): загружает rubrics из БД, вызывает selectRubric перед генерацией
- buildCoverPrompt(): принимает rubric — рубрика задаёт весь визуальный язык
- Убраны лишние ограничения (no circuit boards, no glowing nodes, no brains)
  из базового промпта — теперь только: no text, no logos, no real faces

regen-covers.js

@@ -0,0 +1,32 @@
+require('dotenv').config({ path: '/var/www/zeropost-engine/.env' });
+process.chdir('/var/www/zeropost-engine');
+
+const covers = require('./src/services/covers');
+const config = require('./src/config');
+const { query } = require('./src/config/db');
+
+const DELAY_MS = 8000;
+const sleep = ms => new Promise(r => setTimeout(r, ms));
+
+(async () => {
+  await config.reloadAi();
+  const { rows } = await query('SELECT id, title, tags FROM articles WHERE cover_url IS NOT NULL ORDER BY id');
+  console.log(`Total articles: ${rows.length}`);
+
+  let ok = 0, fail = 0;
+  for (const a of rows) {
+    try {
+      console.log(`\n[${ok+fail+1}/${rows.length}] article=${a.id}: ${a.title.slice(0,60)}`);
+      const url = await covers.generateCover({ articleId: a.id, title: a.title, tags: a.tags||[], channelId: 1 });
+      console.log(`  ✓ ${url}`);
+      ok++;
+    } catch(e) {
+      console.log(`  ✗ FAIL: ${e.message.slice(0,100)}`);
+      fail++;
+    }
+    if (ok + fail < rows.length) await sleep(DELAY_MS);
+  }
+
+  console.log(`\nDone: ${ok} OK, ${fail} failed`);
+  process.exit(0);
+})().catch(e => { console.error(e); process.exit(1); });