fix(web): keep ineligible message forks disabled

apps/web/tests/snapshots/steering/settled.expected.md

@@ -7,6 +7,9 @@
 - text: Use the ask_user_question tool to ask me exactly one question with id "checkpoint", question "Ready to continue?", header "Checkpoint", and options labeled "Yes" and "No". After I answer, reply with one short sentence acknowledging my answer and stop. {{clock}}
 - button "Copy":
   - img
+- button "Branch into a new conversation" [disabled]:
+  - img
+- text: Available only on the last message of a completed turn
 - button "Context injection":
   - img
   - img
@@ -22,6 +25,9 @@
 - text: "Interjection: include the word BANANA in your final reply. {{clock}}"
 - button "Copy":
   - img
+- button "Branch into a new conversation" [disabled]:
+  - img
+- text: Available only on the last message of a completed turn
 - button "Think The user selected \"Yes\" and wants me to include the word \"BANANA\" in my final reply. Let me acknowledge their answer.":
   - img
   - img