(budget layout) FAQ-and-Troubleshooting.md: budgets instead of scenarios, new page links
(retire ages) FAQ-and-Troubleshooting.md: separate retirement ages
(desktop app) FAQ-and-Troubleshooting.md: link the Desktop App page
(window end) FAQ-and-Troubleshooting.md: document plan.last_month
(wiki docs) FAQ-and-Troubleshooting.md: documentation page