Injection token holding the app-wide TreetableConfig. The
default factory returns an empty object, so consumers can call
inject(CNGX_TREETABLE_CONFIG) without first calling
provideTreetable() - they just get the library defaults.
CngxTreetable already injects this internally to build the
resolvedOptions cascade; reach for it directly only when you are
writing a sibling component that needs to honour the same app-wide
defaults.