Add AI-powered price extraction fallback

- Add AI extraction service supporting Anthropic (Claude) and OpenAI
- Add AI settings UI in Settings page with provider selection
- Add database migration for AI settings columns
- Integrate AI fallback into scraper when standard methods fail
- Add API endpoints for AI settings and test extraction

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/package.json

@@ -10,6 +10,7 @@
     "db:init": "tsx src/config/init-db.ts"
   },
   "dependencies": {
+    "@anthropic-ai/sdk": "^0.24.0",
     "axios": "^1.6.0",
     "bcrypt": "^5.1.1",
     "cheerio": "^1.0.0-rc.12",
@@ -18,6 +19,7 @@
     "express": "^4.18.2",
     "jsonwebtoken": "^9.0.2",
     "node-cron": "^3.0.3",
+    "openai": "^4.47.0",
     "pg": "^8.11.3",
     "puppeteer": "^22.0.0",
     "puppeteer-extra": "^3.3.6",