fix(Tooltip): render above the overlay tier so tooltips aren't occluded

[DreaminDani]

Problem

Tooltip content has no z-index, while Dropdown, Menu, ContextMenu and DatePicker all set z-index: 1. When a tooltip's trigger sits inside one of those overlays, the tooltip portals into the same stacking context with an effective z-index: auto (0) and renders behind the overlay.

This is now easy to hit because EllipsisContent shows a real Tooltip on overflow: an EllipsisContent placed inside a Dropdown (e.g. a truncated label in a menu item) shows its tooltip clipped behind the menu.

Fix

Give tooltip content z-index: 2 so it sits just above the z-index: 1 overlay tier. Toast remains at the top (2147483647).

.content {
  /* Sit above the z-index:1 overlay tier (Dropdown, Menu, ContextMenu, DatePicker)
     so a tooltip triggered from inside one of them isn't occluded by it. */
  z-index: 2;
  ...
}

Verification

Render an EllipsisContent with overflowing text inside an open Dropdown and hover the trigger — the tooltip now paints above the menu instead of behind it. Existing Tooltip/EllipsisContent stories and visual-regression baselines cover the rendering.

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[XOP]

@DreaminDani Please add screenshots / recording for problem illustration; when applicable please include before/after media.

📝 Follow up for the future - we should add a group of z-index tokens to operate semantic values vs absolute/hardcoded ones

[DreaminDani]

@XOP

Please add screenshots

Added :)

Follow up for the future

I made an internal ticket for this, for now. We can revisit when we're looking at other tokens.