Fix product tour selector picker and no-match fallback

Picker (GleapAdminHelper): walk up to 3 ancestors looking for
`data-gleap-tour` so a click on an inner icon/span inside a tagged
wrapper still picks the wrapper's selector instead of falling through
to a class-based unique() selector. Bounded so a high-level layout
wrapper carrying the attribute can't hijack unrelated descendant
clicks.

Runtime (GleapTours): when a step declared a selector but it can't be
resolved after the 5s retry window, fail the tour cleanly via
onElementNotFound (fires productTourQuit) and warn in console, instead
of silently re-anchoring the popover to a hidden dummy element at the
center of the screen. The dummy-element fallback is preserved for
legitimate "info" message steps that have no selector at all.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: floooat