Add EUR reporting view to investments #165

Goal

View investments in EUR as well as HUF and USD, including gains, history and trade previews.

Current behavior

The Investments reporting selector and session state support HUF/USD only. The overview requests those two reporting ledgers, and the API caps each metrics/preview read at two currencies.

Desired behavior

Add EUR to the same selector and session-memory state. Load HUF/USD/EUR metrics together, apply the existing dated-cost/current-value rules, request history in the selected currency and show matching detail/trade previews. Native instrument prices remain in their actual quote currency.

Acceptance criteria

• EUR selection updates summary, holdings, allocation, details, history and trade preview; selection survives route changes in session memory.
• API accepts up to three supported reporting currencies, with unchanged default compatibility and bounded reads.
• Missing EUR metrics cannot publish a partial overview; failed EUR history remains separate from other currency snapshots.
• Relevant client/API/Worker tests and type/build/lint checks pass; restored local database reads preserve financial facts.

References or visuals

Under #123, Investment Page Rework milestone. No schema change, currency inference or production writes.