Adds a second historical line to the existing cash-balance chart showing
what the balance would be if all outstanding player dues were paid,
reconstructed per month the same way the existing balance line is.
Approved plan for the three overview charts (balance history, monthly
income/expense, top-10 outstanding players): new backend aggregation
endpoint plus a chart.js-based frontend integration on the existing
overview page.
Brainstormed with the user: three charts on the existing overview page
(balance history, monthly income/expense, top-10 outstanding players),
Chart.js as dependency-free charting lib, new backend aggregation
endpoint since none of the existing endpoints group transactions by
time or category.
.env already exists locally with valid creds (the deleted repo-root
.env was an unused duplicate), and no MailDev infra exists for the
e2e mail tests, so the plan shifts to a MailService unit test plus
one manual send instead of touching .env or standing up e2e infra.
Captures the brainstorming outcome for fixing the broken mail dispatch,
removing the mail-only nestjs-i18n setup in favor of hardcoded German
copy, and redesigning the registration/forgot-password email templates.
