** You must render the charts under the div html element with id {{ chart_element_id }}.
** Add a custom mode bar button named "Fullscreen" that toggles the chart container in and out of fullscreen using the Fullscreen API. Requirements for this button:
* Always call the Fullscreen API on the chart container div itself (document.getElementById("{{ chart_element_id }}")), not on the document or on Plotly’s SVG.
* Use el.requestFullscreen() with fallbacks to el.webkitRequestFullscreen || el.msRequestFullscreen.
* Exit fullscreen with document.exitFullscreen() and vendor fallbacks.
* Listen for fullscreenchange, webkitfullscreenchange, and msfullscreenchange to keep the button working across repeated clicks and ESC exits.
* Ensure the chart fully expands and scales to the entire screen when fullscreen is active.
* Provide a simple inline SVG path icon for the button (no external assets).
* Use Plotly.newPlot(container, data, layout, {displayModeBar:true, modeBarButtonsToAdd:[fullscreenBtn]});
* fullscreenBtn must be a fully-formed object {name, title, icon, click}.