* feat(reports): add Period Return card to Investment Performance tab
Surfaces market-only return (absolute + %) for the selected period using
net_market_flows from the balances table, excluding contributions and
withdrawals. Appears in both the interactive report and the print view.
* docs: remove TODOS.md; fold FX fallback caveat into PR description
The single V2 item (Period Return's 1:1 FX fallback on missing rates) is
now documented under Known Limitations in the PR description, so a tracked
file in the repo root is redundant.
* fix(investment_statement): align start_value denominator scope and FX handling
Add status filter to match absolute_return, and move FX conversion into
SQL so pre-period balances are found even when an account's currency was
changed after balances were recorded.
