Adds full frontend-only Investment module mirroring the legacy AutoBank CBS
Investment menu: Dashboard, FD/Bond/Share entry screens (purchase, interest,
sell/redeem, write-off, amortize and more), 10 master screens, an Interest
calculation/register screen, and ~21 reports. All figures are derived from a
single holdings/transactions dataset so entry, interest, and reports can
never drift out of sync. Wires the new "Investment" mega-menu into the shell
and routes the previously inert Investment stub buttons.
