Update nav to use `aria-[current=page]` classes for active styles

[Tpbradley]

Moved from realmacsoftware/RapidWeaver#3897 — Core Pack components live here (Tom 7 Sep 2026).

https://x.com/adamwathan/status/1862873672911925340

[Tpbradley]

Moved from RapidWeaver #3897: https://github.com/realmacsoftware/RapidWeaver/issues/3897