docs: rewrite README to highlight report dashboard and strategy creation

- Restructure README around create → backtest → compare → deploy loop
- Add detailed Backtest Report Dashboard section (overview + compare pages)
- Shorten strategy example from ~200 lines to ~30 lines
- Move sponsor section into header with styled layout
- Clean up features table and remove emoji clutter
- Fix test tuple order in test_backtest_report_html.py (value, date)

Author: MDUYN