fix(desktop): show diagnostics when backend startup keeps failing#23862

fix(desktop): evidence capture fails when the recording is missing or truncated

fix(desktop): evidence capture drops an inherited VITE_DEV_SERVER_URL

fix(desktop): explicit stop resets the backend start-failure streak

test(desktop): capture fixture restores the checkout on SIGTERM and records real sources

Merge main into fix/issue-10517

test(desktop): add native backend startup capture fixture

fix(desktop): repeated backend start failures offer copyable diagnostics without pausing restarts

fix(desktop): a primary backend crash loop now shows why it can't start

test(desktop): primary backend crash-loop before readiness shows no error