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

backend/src/config.ts

@@ -76,6 +76,14 @@ export const config = {
   depositLightningAddress: process.env.DEPOSIT_LIGHTNING_ADDRESS ?? "",
   depositLnurlp: process.env.DEPOSIT_LNURLP ?? "",
   cashuRedeemApiUrl: (process.env.CASHU_REDEEM_API_URL ?? "https://cashu-redeem.azzamo.net").replace(/\/$/, ""),
+
+  // Sponsors
+  baseSponsorPricePerDay: envInt("BASE_SPONSOR_PRICE_PER_DAY", 200),
+  sponsorMaxActivePerUser: envInt("SPONSOR_MAX_ACTIVE_PER_USER", 5),
+  sponsorMaxVisible: envInt("SPONSOR_MAX_VISIBLE", 6),
+  adminPubkeys: (process.env.ADMIN_PUBKEYS ?? "").split(",").map((s) => s.trim()).filter(Boolean),
+  /** Public API base URL for LNbits webhook (e.g. https://api.example.com). Required for sponsor payments. */
+  publicApiUrl: (process.env.PUBLIC_API_URL ?? process.env.FRONTEND_URL ?? "").replace(/\/$/, ""),
 };
 
 export function usePostgres(): boolean {