Let me edit the agent's proposed content inline before authorizing the action

## Request

Let me edit the agent's proposed content inline in the chat, then authorize it — instead of spending a full turn describing a tiny fix.

## Example

I ask: **"Update my GitHub profile."** The agent replies with proposed bio text that's almost perfect, but the last sentence needs to go. Today I have to write a follow-up ("drop the last sentence") and wait for the agent to regenerate. Instead, I want to delete that sentence directly in the agent's message and just say **"make the update"** — and the agent uses my edited version as the input to its action.

## Why this is different from existing requests

- **Not** user-message editing (#1602) — that re-runs my prompt and discards the agent's output.
- **Not** diff editing (#1397) — here the content lives only in the chat message; nothing is on disk yet.

The agent's message is sometimes the deliverable itself. Treat it as an editable draft I can amend before authorizing the action (like editing an AI-drafted email before hitting send).

Beginne damit, den in der Anfrage beschriebenen Ablauf von Chat-Nachrichten und Aktionsautorisierung nachzuverfolgen. Fertig ist die Arbeit, wenn ein Benutzer vorgeschlagene Agenteninhalte inline bearbeiten, die Aktion autorisieren und die Aktion die bearbeitete Version statt des ursprünglichen Entwurfs verwenden kann.

Vom Indexierungsmodell aus dem Issue-Text verfasst.