feat(ui): render ending lines distinctly and lock input on end-state

Ending-kind lines get a separator and italic styling. Once endedWith is
set, the terminal disables the input and rejects all commands except
restart and undo.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/ui/crt.css

@@ -169,3 +169,17 @@
 @media (pointer: coarse) {
   .mystery-chips { display: flex; }
 }
+
+.mystery-transcript .ending {
+  margin-top: 2em;
+  margin-bottom: 1em;
+  padding-top: 1em;
+  border-top: 1px solid currentColor;
+  font-style: italic;
+  white-space: pre-wrap;
+}
+
+[data-mystery-input]:disabled {
+  opacity: 0.4;
+  cursor: not-allowed;
+}