fix: the first wallet's first address is active as soon as it is added (closes #512)

The popup picked an active address only when it opened, so after the first
wallet was created nothing was active until a reopen: Home had no headline,
and Send and Receive refused. Each of the three import paths on AddWallet now
makes the new wallet's first address active when no address is. When the
phrase or xprv scan then replaces the address list with one that leaves that
address out, the new list's first address becomes active and the background
is told, as when the user picks an address on Home. The address scan stand-in
in the popup test boot now answers in the real scan's shape, which the phrase
and xprv imports read.

Model: opus-5-5

tests/support/popupBoot.js

@@ -258,12 +258,17 @@ async function bootPopup(stored, options) {
         formatAddressTotal: () => "",
         getAddressValue: () => ({ usd: null, partial: false }),
     }));
+    // scanForAddresses() answers in the real one's shape, a scan that found
+    // no used address: AddWallet reads `addresses` from it.
     jest.doMock("../../src/shared/balances", () => ({
         fetchTokenBalances: jest.fn(async () => []),
         refreshBalances: jest.fn(async () => {}),
         lookupTokenInfo: jest.fn(async () => null),
         getProvider: () => ({}),
-        scanForAddresses: jest.fn(async () => []),
+        scanForAddresses: jest.fn(async () => ({
+            addresses: [],
+            nextIndex: 1,
+        })),
     }));
     // filterTransactions() answers in the real one's shape: Home,
     // AddressDetail and AddressToken read both fields, and a bare list makes