- Add chart type selector with 3 chart types: candlestick (default), line, and bar
- Fix data format conversion when switching between OHLC and simple {time,value} formats
- Fix line chart refresh to use update() instead of setData() to preserve chart data
- Remove area chart type and AI Insight/refresh buttons
- Improve data handling in loadData, loadNewData, loadHistoricalData, and switchChartType methods