Prevent infinite recursion in custom navigation modules (#18)

A customnav module returns its configured page selection irrespective of
the requested parent page. When a selected page has subpages, the builder
recursed into the same selection and could loop indefinitely. Skip subpage
retrieval for custom navigations by default and expose the knp_skip_subpages
option to control it (prefixed to avoid clashing with page fields).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Bump depenencies

Remove 0 values from trail

Fix: Undefined array key

Fix: CS

Correctly include subpages in result set (#12)

Work around dropped method findPublishedSubpagesWithoutGuestsByPid (#11)

Add FrontendMenuEvent (#10)

CS

Bump dependencies