feat: implement master key derivation and persistence via IndexedDB

frontend/src/utils/keystore.ts

@@ -0,0 +1,17 @@
+import { openDB } from "idb";
+
+// we use this to store master key in browser - secure and good UX
+const db = openDB("piku-keys", 1, {
+  upgrade(db) {
+    db.createObjectStore("master-key");
+  },
+});
+
+export const saveMasterKey = async (key: CryptoKey) =>
+  (await db).put("master-key", key, "masterKey");
+
+export const loadMasterKey = async (): Promise<CryptoKey | null> =>
+  (await db).get("master-key", "masterKey") ?? null;
+
+export const clearMasterKey = async () =>
+  (await db).delete("master-key", "masterKey");