Remove hardcoded invoke suggestion from azd ai agent run

[Copilot]

azd ai agent run was printing a static azd ai agent invoke --local "Hello!" suggestion that is incorrect for agents using the /invocations protocol — the payload shape is agent-specific and "Hello!" is not a valid invocation body in most cases, leading to confusing runtime errors.

Changes

• runRun(): Remove the three-line "After startup, in another terminal, try: …" block; retain only the Starting agent on http://localhost:<port> (Ctrl+C to stop) line.
• newRunCommand() Long description: Remove the trailing "Use a separate terminal to invoke the running agent: …" paragraph for the same reason.

[jongio]

Changes look correct - removes the hardcoded "Hello!" suggestion that doesn't match most agent protocols.

Both locations (the Long description and the runtime fmt.Printf output) are cleaned up. The remaining \n prefix on the Printf properly preserves blank-line spacing. No test impact.

Minor note: invoke.go:63 still shows azd ai agent invoke --local "Hello!" in the invoke command's own examples. That's a different context (documenting invoke's syntax vs suggesting a specific payload from run), but worth considering whether the invoke examples should also use a more protocol-appropriate placeholder.