[No QA] Docs updates for E/A#95631 agent creation opens the agent DM immediately

[MelvinBot]

Explanation of Change

Help site update prompted by Expensify/App#95631 ("Open the agent DM via an optimistic reportID").

That PR changed what happens right after you create an agent: instead of returning you to the Agents list, the app now takes you directly into a DM with the new agent, where the agent's welcome message appears once it arrives.

This updates Create-and-Use-Custom-Agents.md to reflect the new post-creation behavior:

• How to create an Agent — the outcome line now states you're taken directly to a DM with the new agent (it still notes the agent also appears in the Agents list with Edit, Chat, and Copilot buttons).
• What happens after you create an agent — added a bullet noting you land directly in the agent's DM.

UI labels (New agent, Build custom agent, Write custom instructions, Create agent, Agents) were verified against the live web UI.

Fixed Issues

$

Screenshots

Agents (Beta) page

Build custom agent screen

Immediately after clicking Create agent — the new agent's DM opens

Agent also appears in the Agents list afterward

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@mjasikowski, please review the files changed and confirm they reflect the current behavior. Then post a new comment saying @MelvinBot mark this PR as ready for review.

[OSBotify]

A preview of your ExpensifyHelp changes have been deployed to https://b43bf9f0.helpdot.pages.dev ⚡️

Updated articles:

• articles/new-expensify/ai-agents/Create-and-Use-Custom-Agents