docs: rename IT Helpdesk Agent to IT Support Agent

[mwbrooks]

Summary

This pull request renames "IT Helpdesk Agent" to "IT Support Agent" across all READMEs, documentation, and the App Home greeting.

• Renames "IT Helpdesk" to "IT Support" in titles, descriptions, and project structure sections.
• Updates the App Home greeting from "your IT helpdesk agent" to "your IT support agent".

Testing

• Run the app and confirm the App Home greeting says "IT support agent".
• Confirm READMEs render correctly on GitHub.