webui: future-forecast mode with TradingView-style chart interaction

[rishab-bf]

What changed

Reworks the web UI prediction flow around forecasting forward from the latest data, and makes the chart behave like a standard trading chart.

Forecasting

• Predictions now use the most recent 400 bars in the file and forecast 120 bars beyond its end, instead of requiring a 400+120 backtest window inside the data.
• The forecast is anchored 2 trading days back, so its first bars overlap known candles - users get an immediate visual quality check of the model against reality before the true-future portion begins. The overlapping bars also feed the existing predicted-vs-actual comparison table.
• Future timestamps are session-aware (make_future_timestamps): daily data advances over business days; intraday data stays inside the observed session (e.g. 09:15-15:30) and rolls to the next business day.

Chart

• Forecast renders as blue/purple candlesticks, visually distinct from the teal/red actual candles; a dotted divider with a "Forecast starts here" annotation marks the boundary.
• TradingView-style interaction: scroll-wheel zoom, drag to pan, double-click to reset, and the price axis auto-fits the visible candles on every x-range change (autoFitY relayout handler).
• Non-trading time is removed from the axis via rangebreaks: weekends, market holidays auto-detected from gaps in the loaded data, and overnight hours for intraday files.
• Chart fills the viewport height, opens zoomed to the last ~60 bars + forecast, and the legend sits below the plot so candles get the full panel width.

Misc

• Server port is configurable via KRONOS_WEBUI_PORT (default 8090) for machines where 7070 is occupied; the Werkzeug reloader is disabled to avoid duplicate model loads.
• The fixed 400+120 time-window slider is hidden (superseded by the always-latest forecast flow).

Why

The previous UI could only "re-predict the past" for comparison; there was no way to get an actual forward forecast from the latest bar, which is the primary thing users ask of the model. Tested end-to-end on NSE (Indian market) daily and 5-minute data.

Notes for reviewers

• Frontend still uses the bundled plotly.js v1.58 via CDN; rangebreaks and scrollZoom are supported there and were verified working.
• create_prediction_chart keeps backward compatibility with the old backtest-window path (start_date), which the API still accepts.

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