Stop showing inaccurate payload hints after `azd ai agent run`

[therealjohn]

Goal

Don't show the wrong payload suggestion during run.

Context

Current Behavior

The run command shows a static message on how to use invoke, but for the /invocations API this is typically not accurate and leads to confusing errors at runtime.

Desired Behavior

Remove this suggestion completely now that /invocations exists. There's currently no way to know the right payload shape and developers will need to read the README.md for examples.

Implementation Notes

• Do not include any static or hard coded messages.

Acceptance Criteria

• Unit tests added or updated
• Existing test suite passes
• Lint or format passes

How to Test

azd ai agent run
Should not see any "After startup, in another terminal, try:" messages.