TUI: Add confirmation dialogs for destructive actions

[mihaelamj]

Summary

Prevent accidental destructive operations with confirmation dialogs.

Use Cases

• Saving selections (overwrite existing priority-packages.json)
• Clearing all selections
• Changing base directory

Design

┌────────────────────────────────────────────┐
│            Confirm Action                  │
├────────────────────────────────────────────┤
│                                            │
│  Save 42 selected packages?                │
│                                            │
│  This will overwrite:                      │
│  priority-packages.json                    │
│                                            │
│  [Y] Yes, save    [N] Cancel               │
│                                            │
└────────────────────────────────────────────┘

Tasks

• Create ConfirmDialog.swift component
• Add dialog rendering overlay
• Handle Y/N input for confirmation
• Add confirmation before overwrite operations
• Test dialog rendering and input handling

Files

• Sources/TUI/Components/ConfirmDialog.swift (new)
• Sources/TUI/PackageCurator.swift
• Sources/TUI/Models/AppState.swift