Page 3 (Blue AV Envelope Order Form) now shows only when the purple
envelope stock question is answered "KCI's stock" - choosing "My own
stock" skips it, since KCI wouldn't be sourcing envelopes either way.
Falls back to visible if that question was never reached.

Also sets clearInvisibleValues: "onHidden" on the survey so answers to
a question don't linger after the question that revealed it gets
changed back (e.g. flipping "purchase blue AV envelopes?" from Yes to
No no longer leaves the permit/nonprofit-status answers underneath it
in place) - applies to every conditional branch on the form, not just
this one.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>