Add remote autopilot install slash command

[noureldin-azzab]

Summary

• add /remote-autopilot-install command for installing Stakpak Autopilot on remote Linux hosts
• support existing SSH hosts plus AWS/GCP/Azure discovery and provisioning flows
• include provider-neutral placement/capacity preflight for VM creation
• include Slack/Telegram/Discord channel setup, with Slack manifest guidance
• invoke the pinned public bootstrap installer script from GitHub raw

Validation

• git diff --check
• command markdown frontmatter check
• command-specific content checks