feat: add Supabase vendor data integration (BSR, ratings, buy box)

- Create vendor_daily_data table schema and Supabase client service
- Add upload API route for Vendor Central CSV parsing and upsert
- Add VendorDataView with BSR trend, ratings, and buy box charts
- Integrate new Vendor tab into app navigation (desktop + mobile)
- Add vendor CSV upload card to FileUpload modal

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

package.json

@@ -13,6 +13,7 @@
   },
   "dependencies": {
     "@google/genai": "^1.30.0",
+    "@supabase/supabase-js": "^2.97.0",
     "node-fetch": "^3.3.2",
     "papaparse": "^5.5.3",
     "react": "^19.2.0",
@@ -27,4 +28,4 @@
     "typescript": "~5.8.2",
     "vite": "^6.2.0"
   }
-}
+}