Retire the git diff theme

README.md

@@ -5,8 +5,7 @@ Typing practice in your terminal.
 ![TermType — the cozy theme](docs/termtype-cozy.gif)
 
 - **Seven themes** — from a warm minimal screen (`cozy`, the default) to a
-  log stream, a Matrix rain, a git diff, a hex editor, and a live Claude
-  Code session.
+  log stream, a Matrix rain, a hex editor, and a live Claude Code session.
 - **Sentences or words** — the built-in sentence pool, or a random stream
   of common English words.
 - **Normal and Time Attack** — untimed rounds, or a 15/30/60-second race.
@@ -103,7 +102,6 @@ It is auto-enabled for non-UTF-8 locales, or force it with
 - `simple` — a plain, clean screen.
 - `matrix` — green rain, inspired by The Matrix.
 - `hex` — mimics a hex editor.
-- `diff` — looks like a git diff.
 - `claude` — composing a message in a live Claude Code session.
 - `tutor` — a touch-typing tutor: a finger-zone-colored keyboard with the
   next key highlighted, and a pair of hands pointing at the finger to use.

cmd/termtype/menu_test.go

@@ -97,3 +97,10 @@ func TestRestoresSavedTheme(t *testing.T) {
 		t.Fatalf("idx = %d, want %d (saved theme not restored)", got, want)
 	}
 }
+
+func TestRemovedThemeFallsBackToCozy(t *testing.T) {
+	m := newMenuModel("diff") // 구버전 config에 남아 있을 수 있는 값
+	if got := m.themes[m.idx]; got != "cozy" {
+		t.Errorf("removed theme should fall back to cozy, got %q", got)
+	}
+}