feat(dashboards): agents landing page as a dashboard

[bcoe]

WIP, demonstrating that it's easy to move agent / mcp pages over to dashboards piece by piece.

Problems Noticed:

• LLM Calls / Tokens Used / Tools Called charts have "Other" category with most of the spans, this problem does not happen in explore. 👈 the problem here was that I hadn't set a descending sort order for the chart.
• Errors and Traffic are very different scales, this chart would benefit from two axis (so both series are visible).
• I'm not 100% sure how we will show a "Trace" table (we usually show transaction tables throughout the rest of the product, it's a matter of how we find the trace roots).

Todo

• Clicking a trace identifier should show a custom trace slide-out.

[bcoe]

@obostjancic I started putting this together as an exercise based on @DominikB2014 document, hoping it would start the discussion about how we convert these page and find some bugs.