Add accessible chart summaries

[JSE19]

DS-074: Add accessible chart summaries and data-table fallback

Context
The candlestick chart (TVChartContainer) renders via Lightweight Charts canvas, which is opaque to screen readers. Assistive technology users could not discover the chart's time range, trend, latest value, or underlying sampled data.'

Changes
apps/web/src/features/trade/components/chart/TVChart.tsx

• Added role="status" to the "Select a market" empty state so screen readers announce when no market is selected.
  apps/web/src/features/trade/components/chart/TVChartContainer.tsx
• Accessible summary: Added VisuallyHidden region (id="chart-desc") with symbol, period, date range, latest price, and trend direction. The chart container now has role="img", aria-label, and aria-describedby pointing to the summary.
• Data-table fallback: Added a keyboard-reachable toggle button that reveals a semantic with /

  headers (Time, Open, High, Low, Close) and up to 15 representative OHLC rows in chronological order. Throttled live announcements: Integrated LiveRegion + useAnnouncer to announce price updates at a throttled cadence (max 1 per 5 seconds, mode="polite"). State handling: Loading, empty, and error states now have equivalent visible text with appropriate ARIA roles (status, alert). The canvas wrapper is aria-hidden when no data is available. Internal helpers: getChartSummary() computes the accessible description from candle data; getRepresentativeRows() samples evenly-spaced candles to avoid giant tables. apps/web/src/features/trade/components/chart/TVChartContainer.test.tsx (new) 16 tests covering: summary content (symbol, period, latest price, trend detection), chart role/label, data-table semantics (column headers, table elements, chronological order, toggle behavior, row limits), announcement throttling (within and after the throttle window), and loading/empty/error states. Acceptance criteria met Chart has accessible name, description, time range, and latest value Data fallback uses semantic table headers and chronological rows Live updates do not announce every tick (5 s throttle) Loading, empty, and error chart states have equivalent text Tests cover summary content, table semantics, and announcement throttling Closes DS-074: Add accessible chart summaries and data-table fallback #474

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