[Fix] Denomination 3 characters (#3001)

* fix: denomination must be 3 chars ISO

lnbits/core/templates/admin/_tab_theme.html

@@ -61,6 +61,7 @@
             v-model="formData.lnbits_denomination"
             label="sats"
             :hint="$t('denomination_hint')"
+            :rules="[(val) => !val || val.length = 3 || val === 'sats' || $t('denomination_error')]"
           ></q-input>
         </div>
         <div class="col-12 col-md-4">

lnbits/static/i18n/en.js

@@ -483,6 +483,7 @@ window.localisation.en = {
   lnbits_wallet: 'LNbits wallet',
   denomination: 'Denomination',
   denomination_hint: 'The name for the FakeWallet token',
+  denomination_error: 'Denomination must be 3 characters, or `sats`',
   ui_qr_code_logo: 'QR Code Logo',
   ui_qr_code_logo_hint: 'URL to logo image in QR code',
   ui_custom_image: 'Custom Image',