fix: scrapers status endpoint — correct table and column names
- Replace vendor_slug → vendors.slug via JOIN (column doesn't exist on transceivers)
- Replace competitor_prices + ebay_listings → price_observations (correct table)
- Replace market_intelligence → knowledge_base in status DB stats (table exists, 73 rows)
- price_observations columns: transceiver_id, price, time (not part_number/price_eur/scraped_at)
- Result: 5602 transceivers, 359 vendors, 465 switches, 4252 prices, 73 KB entries all visible
69ef507d8a