feat: improve nwc qr code ux

app/src/main/java/com/bitcointxoko/gudariwallet/api/Models.kt

@@ -330,7 +330,7 @@ data class NwcKey(
     val wallet: String,
     val description: String,
     val expires_at: Long,
-    val permissions: String,       // comma-separated permission names
+    val permissions: String,
     val created_at: Long,
     val last_used: Long
 )
@@ -352,7 +352,8 @@ data class NwcGetResponse(
 
 data class NwcNewBudget(
     val budget_msats: Long,
-    val refresh_window: Int        // seconds
+    val refresh_window: Int,        // seconds
+    val created_at    : Long = System.currentTimeMillis() / 1000L
 )
 
 /** Request body for PUT /nwc/{pubkey} */