custom flag (2) (#1303)

## Description:

This PR implements the permission check logic.

Other related parts will be handled in a separate UI update.

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced
- [x] I understand that submitting code with bugs that could have been
caught through manual testing blocks releases and new features for all
contributors

src/client/TerritoryPatternsModal.ts

@@ -1,3 +1,4 @@
+import { base64url } from "jose";
 import type { TemplateResult } from "lit";
 import { html, LitElement, render } from "lit";
 import { customElement, query, state } from "lit/decorators.js";
@@ -369,7 +370,10 @@ export function generatePreviewDataUrl(
   height?: number,
 ): string {
   // Calculate canvas size
-  const decoder = new PatternDecoder(pattern ?? DEFAULT_PATTERN_B64);
+  const decoder = new PatternDecoder(
+    pattern ?? DEFAULT_PATTERN_B64,
+    base64url.decode,
+  );
   const scaledWidth = decoder.scaledWidth();
   const scaledHeight = decoder.scaledHeight();