fix: prevent tooltips from being scrollable

[djanhjo]

Prevent tooltips from being scrollable, since they should be sized to whatever content they have. Also initialize with height: 0 to prevent initial load of empty scrollable space.

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Note

Low Risk
Small tooltip markup/CSS change with no auth, data, or API impact; height is still set by existing resize logic.

Overview
Tooltip iframes were showing scrollbars and reserving empty scrollable area before content sized them.

The tooltip template now sets .gist-tooltip-frame to height: 0 until resizeTooltipComponent applies the content height (existing height transition unchanged), and adds scrolling="no" on the tooltip iframe so it does not scroll independently of the sized content.

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