Improve Runtime TUI contextual actions

[aidandaly24]

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.