[FEATURE] Emoji reactions (👍) on assistant messages

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet — closest match is #47906, which was closed by the stale-bot (with 5 👍 and supportive comments) and is now locked; its closing message invites a new issue.
• [x] This is a single feature request (not multiple features)

Problem Statement

In long-running agent sessions, a large share of user turns are pure acknowledgements ("ok", "continue", "looks good"). Typing these breaks the user's flow and costs a full conversation turn just to say "approved". There is currently no lightweight way to acknowledge an assistant message.

(Illustration: to support this very request on GitHub, the user had to type an API call to add a 👍.)

Proposed Solution

Emoji reactions (at minimum 👍) on assistant response blocks in the VSCode extension (where this request originates) and the CLI — a single keypress/click on a response block that the agent receives as an acknowledgement signal, without a typed message.

Alternative Solutions

• Typing short replies ("ok", "continue") — works but interrupts flow and adds noise to the transcript.
• Related: #36574 (emoji picker for chat input) addresses input, not acknowledgement of responses.

Priority

Medium - Would be very helpful