Replaces the hover+pin+timeout implementation with Mantine Popover's built-in uncontrolled behavior (click to open, click outside/escape to close). Removes all component state, mouse handlers, timeout management, and the cross-popover close machinery from the parent. - 56 lines removed, 13 added across 3 files - Border highlight now via CSS aria-expanded selector - Resolves the messy hover navigation issue (#2637)