Add statistics page with time-period revenue charts and cumulative revenue line

[IanTheMitten]

Motivation

• Provide a dedicated statistics view to inspect revenue patterns by canonical time periods and visualize cumulative revenue over sampled sales within a selected period.
• Surface weekday-focused averages and a running total so staff can identify busy windows and revenue trends across days.

Description

• Added a new StatisticPage component at src/components/budget/StatisticPage.tsx that filters transactions by date range and composes two visualizations.
• Implemented TimePeriodRevenueBarChart in src/components/budget/TimePeriodRevenueBarChart.tsx with CANONICAL_PERIODS, getCanonicalPeriodForDate, per-period average revenue calculation (weekdays only), selectable bars, and configurable coloring.
• Implemented TimePeriodCumulativeLine in src/components/budget/TimePeriodCumulativeLine.tsx that samples transactions for the selected canonical period, excludes weekends, and renders a cumulative revenue line chart.
• Wire up navigation and routing: updated TopBar (src/components/TopBar.tsx) to include a new statistics nav item and adjusted its props/types; updated App.tsx to include the statistics page state, import the StatisticPage, and render it when selected.
• Charts use recharts and the existing CurrencyContext formatting for tooltips and labels.

Testing

• No automated tests were run on this change.

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Codex Task