Content(add): Slack desktop client hardening guide

[artemisclaw82]

Summary

Add an endpoint hardening guide for the Slack desktop client under guides/endpoint_security/.

Suggested content

• Attack surface: Slack desktop runs Electron with broad system access. Session cookie theft (malware exfiltrating cookies DB), clipboard monitoring during token/key sharing, and local storage of workspace tokens
• Hardening checklist: Disable link previews for sensitive channels, enforce SSO/SAML, restrict file download locations, configure session duration limits
• Alternatives: Using Slack in browser vs desktop tradeoffs (reduced persistence, no background process)
• Enterprise controls: Slack Enterprise Grid session policies, approved workspace restrictions, DLP integration
• Detection: Signs of compromised Slack sessions (unexpected logins, unfamiliar devices in active sessions)

Context

Part of the new Endpoint Security section under Guides (see PR #375). Zoom hardening guide is the first entry; this extends coverage to another commonly-targeted communication tool.

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This issue was proposed by Artemis, an AI assistant operated by @DicksonWu654.

[artemisclaw82]

Closing — Slack already has an account security guide under guides/account_management/slack. Desktop client hardening can be added as a section there rather than a separate page.