Panel render strategy for <cngx-tab-group>. The panel <div> (the aria-controls target) always stays in the DOM; only its content is
rendered per mode. 'eager' (default) renders every panel's content
up front and toggles visibility via [hidden] - today's behaviour,
byte-identical. 'lazy' renders a panel's content the first time it
is activated and keeps it (keep-alive). 'lazy-destroy' renders only
the active panel's content and destroys it on leave.