Smoke Test

Verifies gem packaging by exercising multiple viewport modes and common APIs.

Used by rake verify_gem to catch broken gem builds.

Features Demonstrated

• Inline viewport: 1-line viewport preserving terminal scrollback

• Fullscreen viewport: Block with borders, layout_split, centered mascot

• Scrollback insertion: insert_before to push content into scrollback

• Scrollback restoration: Cursor positioning after inline viewport exit