infra: add linting and formatting for js projects (#230)

* wip

* wip

* wip

* format

* wip(mobile): lint and format

* cleanup

* nits

* nits

* idiomatic react

* nit

* format all root files

js/desktop/src/hooks/use-object-url.ts

@@ -0,0 +1,23 @@
+import { useEffect, useState } from 'react';
+
+/**
+ * Creates an object URL for a Blob/File and revokes it when the source changes
+ * or the component unmounts. Returns null when given null.
+ */
+export function useObjectUrl(source: Blob | null): string | null {
+  const [url, setUrl] = useState<string | null>(null);
+
+  useEffect(() => {
+    if (!source) return;
+    const objectUrl = URL.createObjectURL(source);
+    // Intended external-resource publish to sync, not a render cascade.
+    // eslint-disable-next-line react-hooks/set-state-in-effect
+    setUrl(objectUrl);
+    return () => {
+      URL.revokeObjectURL(objectUrl);
+      setUrl(null); // in cleanup, not the effect body — so no suppression needed
+    };
+  }, [source]);
+
+  return source ? url : null;
+}