defensive: guard createVaultFromRootKey against the service worker returning undefined (was crashing the receiver session with a minified 't is undefined' TypeError before the real error could surface). Bump to v4.3.16.

@@ -325,7 +325,10 @@325325         const response = (await chrome.runtime.sendMessage({326326           type: "CREATE_VAULT_FROM_ROOT_KEY",327327           payload: { password, rootKeyHex },328-        })) as { ok: boolean; data?: { vaultId?: string }; error?: string };328+        })) as { ok: boolean; data?: { vaultId?: string }; error?: string } | undefined;329+        if (!response) {330+          throw new Error("create_vault_no_response");331+        }329332         if (!response.ok) {330333           throw new Error(response.error ?? "create_vault_failed");331334         }