Improve flow of working with Assistant generated text

Is your feature request related to a problem? Please describe.
Right now if you e.g. want to summarize a piece of text, you need to:

1. Select the text
2. Click on the Assistant icon in the toolbar
3. Click on "Summarize"
4. Be overwhelmed by the full Assistant dialog opening
5. Know you have to click "Summarize" again
6. Wait for it to generate
7. Copy it out manually
8. Paste it in manually

Describe the solution you'd like
This flow we could simplify to:

1. Select the text
2. Click on the Assistant icon in the toolbar
3. Click on "Summarize"
4. See a placeholder (e.g. in an infobox-like element with heading "Summary generated by Nextcloud Assistant") get inserted below the text you are summarizing which shows a progress indicator and automatically pastes the summary.

That flow is vastly simpler and less daunting, while also still clearly communicating that it’s AI-generated.

Additional context
This could be done for the actions like:

• Generate headline (insert above)
• Summarize (insert below?)
• Reformulate text (insert below?)
• Translate (insert below?)

One possible drawback is that you can not easily re-generate a result or have error handling. But as a follow-up we could also add a "re-generate" button.

No source file, test, or entry point is named in the issue. Begin by locating the Assistant toolbar flow for selected text and the listed actions in the JavaScript editor; done means the selected text produces an inline generated result with visible progress and clear AI attribution, without opening the full dialog.