cleanup(web): remove the steering interjection caption

Steering bubbles render as plain user bubbles; a mid-turn steer is
recognizable by its position in the flow. The runtime SteeringMessageNode
projection and pending-steering lifecycle are unchanged.

Partially supersedes the 2026-08-04 context-source and steer marks note;
the new simplification note owns the removal rationale.

apps/web/tests/snapshots/plan-review/approved.expected.md

@@ -5,7 +5,7 @@
     - tab "Chat" [selected]
     - tab "Trajectory"
 - img
-- text: "plan Plan mode on. Use /plan off to leave. Interjection Plan a small change: add a --greeting flag to a CLI. Do not read or write any files. Call exit_plan_mode with a short plan of at most five bullet points. Once the plan is approved, reply with the single word DONE and stop. {{clock}}"
+- text: "plan Plan mode on. Use /plan off to leave. Plan a small change: add a --greeting flag to a CLI. Do not read or write any files. Call exit_plan_mode with a short plan of at most five bullet points. Once the plan is approved, reply with the single word DONE and stop. {{clock}}"
 - button "Copy":
   - img
 - button "Context injection @deepseek-ai/dsh-system-prompt":

apps/web/tests/snapshots/steering/mid-steer.expected.md

@@ -21,7 +21,7 @@
   - img
   - text: Ask question waiting
 - status: Deep diving...
-- text: "Interjection Interjection: include the word BANANA in your final reply."
+- text: "Interjection: include the word BANANA in your final reply."
 - button "Copy":
   - img
 - region "Ready to continue?":

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

@@ -19,7 +19,7 @@
   - img
   - img
   - text: Ask question 1/1 answered
-- text: "Interjection Interjection: include the word BANANA in your final reply. {{clock}}"
+- text: "Interjection: include the word BANANA in your final reply. {{clock}}"
 - button "Copy":
   - img
 - button "Think The user selected \"Yes\" and wants me to include the word \"BANANA\" in my final reply. Let me acknowledge their answer.":