fix(Link): treat ? as a boundary in subroute matching

[nebojsa-peric]

A page carrying query state (e.g. ~/items?filter=x) is still on its href's route, but match="subroute" rejected it: the character after the href was ?, not /. A subroute below the href with a query (~/items/42?tab=log) already matched, which made the bug easy to miss — nav items highlighted on detail pages with query state but went dark on their own list page the moment it carried a filter in the URL. Route matching already tolerates the query string, so Link and Route disagreed about whether the same URL was "on" the route.

The fix is one clause: subroute accepts ? as a boundary character alongside /. equal stays full-string equality (query-routed navs like ~/docs?topic=a vs ?topic=b keep exact matching) and prefix was never affected.

url	href ~/items subroute (before)	after
~/items	active	active
~/items?filter=x	inactive	active
~/items/42?tab=log	active	active
~/items-archive	inactive	inactive

Link.spec.tsx covers all three match modes against exact/query/subroute/sibling-prefix urls, query-carrying hrefs, and the active override. litmus/bugs/link-active-query-string.js renders every scenario through both the old matcher (inlined as a subclass) and the fixed one side by side — flip the import in litmus/index.js to play with it.