UR-Nexus 1.61.0

• Added ur selftest, end-to-end drills for the gap that produced every
  serious defect in recent releases: a module that is correct while something
  between it and the user is not — a wire format, a CLI registration, an exit
  code, a wording choice. The drills deliberately do not import the modules;
  they spawn the shipped binary against real directories and assert on what a
  user would see.
• Five drills run automatically and cover the four defects that reached you:
  memory integrity reporting an unchecked store as verified, the trajectory
  gate printing FAILED while exiting 0, --costs hiding which directory it
  searched, and per-agent attribution itself.
• Drills that need a live model cannot be automated, so they are emitted as
  prompts with the specific observation that separates working from broken —
  "it seemed fine" is how the screenshot bug survived its first report.
• ur selftest run exits non-zero on failure, and a test asserts the drills
  actually fail when pointed at a broken binary. A self-test that cannot fail
  is decoration.