Remove the "halves" cover style again

Tried in macOS Terminal: it does not look good there either.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019reK4DUGYqDUjniWYJvwUW

internal/ui/cover.go

@@ -99,10 +99,6 @@ var (
 	// Coarse, but exact in terminals that draw block elements from the font
 	// with the halves off the cell's middle (macOS Terminal).
 	cellsStyle = coverStyle{"cells", 1, 1, func(int) rune { return ' ' }}
-	// halvesStyle (2×1 pixels): left and right half blocks only. Twice the
-	// detail of cells across, for terminals whose upper and lower halves do not
-	// meet at the middle but whose left and right ones do.
-	halvesStyle = coverStyle{"halves", 2, 1, func(mask int) rune { return [4]rune{' ', '▌', '▐', '█'}[mask] }}
 )
 
 // quadrants[mask] is the glyph that fills the quadrants set in mask
@@ -145,8 +141,6 @@ func coverStyleFor(setting string, env func(string) string) coverStyle {
 		return quadrantStyle
 	case "cells":
 		return cellsStyle
-	case "halves":
-		return halvesStyle
 	}
 	// Terminal.app draws block elements from the font, and their halves do
 	// not meet at the cell's middle: rows of a poster come out uneven.