Identity: Redmine 'Create' click stops with 'a target was found positionally' on most GUI runs #1909

Most Redmine GUI runs stop at the Create click because the target was found only by position. Find why the structural identity didn't resolve (a duplicate button, or the form layout), and make it resolve structurally where it's unambiguous. Keep halting when it's genuinely ambiguous. Data: results/frozen-cf28c2af/redmine.

Found by the API-step generalization experiment (internal#106); data in #1906 under results/. Fix generically (no app-specific code), fail closed, and add a real-app regression test.