fix(web): align the context separator with ToolRow and name the caption

Review follow-ups on the context provenance row:

- the producer name now follows ToolRow's aria-hidden separator dot instead
  of a literal middot inside the text, so the two disclosure rows expose one
  accessible-name shape;
- the English steering caption becomes the noun `Interjection`, parallel to
  the Chinese 插话 and to the label this bubble carried before;
- the history fold gets its own provenance assertion, so the mapping it
  declares separately from TranscriptAdapter is pinned on both sides;
- the superseded-in-part bullet on the no-interjection-chrome note now
  enumerates the third Decision bullet too, whose no-badge and no-IconActions
  clauses had both lapsed.

apps/web/tests/snapshots/code-mode-round/ui.expected.md

@@ -10,10 +10,10 @@
 - button "Branch into a new conversation" [disabled]:
   - img
 - text: Available only on the last message of a completed turn
-- button "Context injection · @deepseek-ai/dsh-system-prompt":
+- button "Context injection @deepseek-ai/dsh-system-prompt":
   - img
   - img
-  - text: Context injection · @deepseek-ai/dsh-system-prompt
+  - text: Context injection @deepseek-ai/dsh-system-prompt
 - 'button "Think The user wants me to write a single `run_code` program that:"':
   - img
   - img