Add sponsors system with time slider, LNbits invoices, and UX improvements

- Sponsors table, LNbits createInvoice, webhook handler
- Sponsor routes: create, homepage, list, my-ads, click, extend, check-payment
- Admin routes for sponsor management
- Frontend: SponsorForm, SponsorTimeSlider, SponsorCard, SponsorsSection
- Sponsors page, My Ads page, homepage sponsor block
- Header login dropdown with My Ads, Create Sponsor
- Transactions integration for sponsor payments
- View/click tracking
- OG meta fetch for sponsor images
- Sponsor modal spacing, invoice polling fallback
- Remove Lightning address and Category fields from sponsor form

Made-with: Cursor

frontend/vite.config.ts

@@ -52,6 +52,9 @@ export default defineConfig(({ mode }) => {
         "/config": { target: backendTarget, changeOrigin: true },
         "/stats": { target: backendTarget, changeOrigin: true },
         "/deposit": { target: backendTarget, changeOrigin: true },
+        "/sponsor/": { target: backendTarget, changeOrigin: true },
+        "/health": { target: backendTarget, changeOrigin: true },
+        "/openapi.json": { target: backendTarget, changeOrigin: true },
       },
     },
   };