Doc: Add namespace reference pages to TOC


The `classes` qhp subproject was missing a namespace selector.

Pick-to: 6.12
Change-Id: I3df0510e5edaeaeb6f7c7b25868f15d554d68df9
Reviewed-by: Alexei Cazacov <alexei.cazacov@qt.io>
commita850bbb5fff86cabca0efcee31ef84df4beca463
parent42fb8c51549e07b144b11809bcc5bff81135a297
authorTopi Reinio <topi.reinio@qt.io>
committerTopi Reinio <topi.reinio@qt.io>
commit timeWed, 21 Oct 2026 07:52:44 +0000