New mail in the other signed-in accounts: counts, a dot, and a notification

With more than one account signed in (#49), mail arriving in one that
isn't in front went unseen until someone switched to it (multi-account
spec, MA-8).

- GET /api/auth/accounts/unread answers the Inbox unread count of each
  account not in front, asked through that account's own session (its
  OAuth token renewed first if due), kept a minute per account.
- The web app asks every two minutes while another account is signed
  in. The account menu shows each one's count beside its name, and the
  avatar carries a dot when any of them has unread mail.
- When a count rises while the app is open and desktop notifications
  are on, a notification names the account ("New mail for
  [email protected]"); clicking it switches to that account. An
  account seen for the first time doesn't notify: its mail was already
  there.

Not in this change: notifications with the app closed, which need each
added account's own Web Push subscription.

New strings (3, English only in the other ten catalogs): "New mail for
{name}", "Unread in the Inbox: {count}", "Account: new mail in another
account". Tests: the server answers the other account's count and
nothing when alone; the client keeps the counts, notifies only on a
rise and only with notifications on. Checked in Chrome against the
mock. typecheck, tests (web 1541, server 277) and build pass.

server/src/accounts.test.ts

@@ -139,3 +139,18 @@ test("an organization that doesn't allow it keeps adding off", async () => {
     delete process.env.MOCK_NO_ADD_ACCOUNTS;
   }
 });
+
+test("inbuxa MA-8: the accounts not in front report their Inbox unread count", async () => {
+  const b = new Browser();
+  await b.signIn("[email protected]", "first-password");
+  // Alone, there is nothing to report
+  assert.deepEqual((await b.call("/api/auth/accounts/unread")).body.accounts, []);
+  await b.signIn("[email protected]", "second-password", true);
+  const res = await b.call("/api/auth/accounts/unread");
+  assert.equal(res.status, 200);
+  assert.equal(res.body.accounts.length, 1, "only the account not in front");
+  const [other] = res.body.accounts;
+  const listed = (await b.accounts()).find((a) => !a.front)!;
+  assert.equal(other.id, listed.id);
+  assert.equal(typeof other.unread, "number", JSON.stringify(res.body));
+});