🩹(all) clear the SonarCloud reliability finding and the lint debt

The SonarCloud gate fails on main, so every commit lands red, and
gh run list hides it: it lists only Actions workflows, and the
failure is an app check run.

Reliability rests on one bug, in test_file_service.py, which wrapped
an assertion in an except Exception re-raised through pytest.fail.
Removing it takes the rating from D to A.

Two pieces of debt ride along. The SDK callback id now comes from
crypto.getRandomValues, since it guards an endpoint with no auth. And
core/tasks gets the __init__.py that lets pylint see it, with the
debt that exposes, which is why #1533 fails lint-back.

src/frontend/src/features/sdk/utils/CallbackIdHandler.ts

@@ -2,9 +2,12 @@ export class CallbackIdHandler {
   private readonly storageKey = 'popup_callback_id'
 
   private generateId(): string {
-    return (
-      Math.random().toString(36).substring(2, 15) +
-      Math.random().toString(36).substring(2, 15)
+    // The id is the only thing guarding /rooms/creation-callback/, which is
+    // unauthenticated, so it comes from the CSPRNG rather than Math.random.
+    const bytes = new Uint8Array(16)
+    crypto.getRandomValues(bytes)
+    return Array.from(bytes, (byte) => byte.toString(16).padStart(2, '0')).join(
+      ''
     )
   }