feat: document the copilot panel

[caalador]

Add documentation for the
copilot panel for observability
that is available in development
mode.

fixes vaadin/observability-kit#394

[github-actions]

Preview Deployment

This PR has been deployed for preview.

URL: https://docs-preview-pr-6019.fly.dev

Changed pages

Added content is highlighted in green; removed content is marked in red on each page.

• tools/observability/copilot-panel — added, +149/-0 lines
• tools/observability/getting-started — modified, +3/-1 lines, 1 removal marker(s)
• tools/observability/insights — modified, +1/-0 lines

Built from f994c43

[heruan]

The page matches the panel closely, down to the verbatim UI strings, the refresh interval, ranking, route grouping, meter rendering and navigation order. Two sentences describe the announcement path that vaadin/observability-kit#398 replaced this week, see inline.

Heads up: #5961 adds a bullet at the same spot in the "See also" list of getting-started.adoc, so whichever merges second will need a small conflict fix.

[heruan]

The cut moved to the browser script together with the announcement, so the server is no longer involved.

Suggested change

	The message is a summary, and the server cuts anything longer than 300 characters.
	The message is a summary, cut to 300 characters when longer.

[heruan]

Since vaadin/observability-kit#398 the script writes the line itself, as a log event on Copilot's event bus. There is no server round trip. Relaying through the server made the log panel show each line twice.

Suggested change

	Copilot's plugin API has no notification of its own, so the line is written by asking the server to send Copilot's own log command; a Copilot that drops it costs you a notification, never the panel.
	Copilot's plugin API has no notification of its own, so the line is written as a log event on Copilot's event bus; a Copilot that drops it costs you a notification, never the panel.