Fix NSAlert window resolution, remove swipe actions, hide decorative icons

[datlechin]

Summary

• Broaden NSAlert window resolution to minimize runModal() usage — try keyWindow, mainWindow, then first visible window before falling back to modal
• Remove iOS-pattern .swipeActions from history panel (delete already available via keyboard and context menu)
• Add .accessibilityHidden(true) to 9 decorative empty-state icons across 5 files

Test plan

• Test SSH connection with unknown host key — verify prompt appears as sheet
• Test SSH password prompt — verify it appears as sheet
• History panel — verify delete works via Delete key and context menu
• Enable VoiceOver — verify empty state icons are not announced