Replace Naive UI popup primitives (dropdown / tooltip)

[nighca]

Background

As part of #3013, we scanned the current naive-ui dependency surface in spx-gui.

A major dependency cluster is the popup / overlay stack built on NPopover and NTooltip.

Current dependency points include:

• src/components/ui/UIDropdown.ts
• src/components/ui/UITooltip.vue
• popup-related helpers in src/components/ui/utils/index.ts

Problem

Our popup primitives currently depend on naive-ui internals and already carry workaround logic:

• UIDropdown is implemented on top of NPopover
• it works around incorrect clickoutside behavior when the trigger itself is clicked
• it queries DOM by generated wrapper class because there is no direct way to get the popover wrapper element
• UITooltip depends on NTooltip
• UITooltip manually adds the __popover__ flag to match naive-ui internal expectations
• tooltip styling currently uses non-scoped global style because the component does not style cleanly through the wrapper
• shared popup detection still depends on n-popover class names

This is exactly the kind of library-specific complexity we want to remove.

Goal

Replace the naive-ui popup primitives with internal implementations that fit XBuilder's requirements directly.

Scope

• replace NPopover usage in UIDropdown
• replace NTooltip usage in UITooltip
• preserve current features such as placement, trigger modes, manual positioning, arrow support, popup container selection, and nested popup behavior
• remove workaround logic tied to naive-ui clickoutside behavior and popover wrapper discovery
• remove naive-ui-specific popup class assumptions from shared UI utilities

Notes

This issue is about dropdown / tooltip style popup primitives. Modal-specific work should be tracked separately.