Explain how to pass a JSON string in the launch command's help text

Users frequently ask how to enter a JSON string as input for the launch (run) command, and this generates a steady stream of customer inquiries.

Add guidance on how to pass a JSON string — quoting/escaping rules and a worked example — directly where the user needs it: the launch command field's help text, tooltip, placeholder, or a similar inline hint, so the answer is discoverable without contacting support.

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Captured while working on branch: feat/FR-3668-substep-3a-fullscreen-modal

JIRA Issue: FR-3676

Locate the launch (run) command field in the web UI and inspect its existing help text, tooltip, placeholder, or inline-hint entry point. Add guidance covering JSON-string quoting and escaping with a worked example, then verify that users can discover it directly in the launch command interface.

Written by the indexing model from the issue text.