feat: display truncated lightning address for winners

- Add truncateLightningAddress utility (shows first 2 chars + ******)
- Backend: Include winner_address in past-wins API response
- Frontend: Display truncated address in past winners list
- Telegram: Add truncated address to draw announcements for transparency

Example: username@blink.sv -> us******@blink.sv

back_end/src/controllers/public.ts

@@ -503,6 +503,23 @@ interface PastWinRow {
   pot_after_fee_sats: number | null;
   buyer_name: string | null;
   serial_number: number | null;
+  winning_lightning_address: string | null;
+}
+
+/**
+ * Truncate lightning address for privacy
+ * "username@blink.sv" -> "us******@blink.sv"
+ */
+function truncateLightningAddress(address: string | null): string | null {
+  if (!address || !address.includes('@')) return address;
+  
+  const [username, domain] = address.split('@');
+  
+  // Show first 2 chars of username, then asterisks
+  const visibleChars = Math.min(2, username.length);
+  const truncatedUsername = username.substring(0, visibleChars) + '******';
+  
+  return `${truncatedUsername}@${domain}`;
 }
 
 /**
@@ -523,6 +540,7 @@ export async function getPastWins(req: Request, res: Response) {
          jc.scheduled_at,
          jc.pot_total_sats,
          jc.pot_after_fee_sats,
+         jc.winning_lightning_address,
          tp.buyer_name,
          t.serial_number
        FROM jackpot_cycles jc
@@ -544,6 +562,7 @@ export async function getPastWins(req: Request, res: Response) {
         ? parseInt(row.pot_after_fee_sats.toString())
         : null,
       winner_name: row.buyer_name || 'Anon',
+      winner_address: truncateLightningAddress(row.winning_lightning_address),
       winning_ticket_serial: row.serial_number
         ? parseInt(row.serial_number.toString())
         : null,