v0.4.0

Breaking: every account-scoped tool now names the account in its response, under one key. monzo_list_pots, monzo_list_transactions and monzo_search_transactions return {"account_type": ..., "pots"/"transactions": [...]} instead of a bare array; monzo_spending gains account_type on all four result shapes; and monzo_sync's per-account details rename account to account_type. An empty array previously carried no trace of which account produced it, so "nothing there" and "wrong account" were indistinguishable. Where no account filter is given the value is null, keeping "all accounts" distinct from a missing key.

Also fixes installs: mcp is capped below 2.0, which no longer ships mcp.server.fastmcp.