Add SSH rsync publishing target

[livid]

Summary

Add an optional SSH rsync publishing target to Planet, letting users sync the generated site to a remote server via rsync over SSH alongside or instead of IPNS publishing.

Features

• SSH rsync toggle and destination in the Publishing settings tab (user@host:/path format)
• SSH key selection — users can select a private key from ~/.ssh/ which gets copied into the app's sandbox container, solving sandbox permission issues without requiring Full Disk Access
• Parallel publishing — IPNS and SSH rsync publish concurrently via withTaskGroup
• Rsync log window — logs all rsync operations to tmp/rsync.log with auto-updating display, error highlighting, and a clear button (accessible via Tools > SSH Rsync Log)
• Error detection — shows a yellow warning banner in the log window when SSH key errors are detected, directing users to select a key in Publishing settings
• Validation — destination format validated on save with user-friendly error alerts

Files changed

• MyPlanetModel.swift — new properties (sshRsyncEnabled, sshRsyncDestination, sshRsyncKeyPath), publishViaSSHRsync method, parallel publish logic
• BackupMyPlanetModel.swift — backup support for new fields
• MyPlanetEditView.swift — Publishing tab UI with toggle, address field, SSH key picker
• PlanetError.swift — InvalidSSHRsyncDestinationError, SSHRsyncPublishError
• KeyboardShortcutHelper.swift — Tools menu entry
• New files: SSHRsync/SSHRsyncLogger.swift, SSHRsync/SSHRsyncLogView.swift