Improve Runtime TUI contextual actions

## Summary

Improve the Runtime TUI so users can act on an already-selected Runtime or endpoint without selecting it again.

## Scope

- Add Invoke to the Runtime details screen.
- Replace the endpoint JSON-only destination with a summary and contextual actions.
- Preserve complete endpoint JSON on a child route.
- Return to the originating details screen when leaving contextual invoke flows.

## Validation

Add focused screen coverage and validate both paths with the live TUI harness.

Start with the Runtime details screen and the endpoint JSON-only destination in the Runtime TUI, then trace the existing routes and invoke flow. Add focused screen coverage and validate both Runtime and endpoint paths with the live TUI harness. Done means selected items expose contextual actions, complete endpoint JSON remains available on a child route, and leaving invoke flows returns to the originating details screen.

Written by the indexing model from the issue text.