feat: add search with preview

internal/ui/legend/legend.go

@@ -57,6 +57,7 @@ func (m Model) View() string {
 				{key: "j/↓", desc: "next cue"},
 				{key: "k/↑", desc: "prev cue"},
 				{key: "ctrl+d/u", desc: "jump 5 cues"},
+				{key: "s", desc: "search"},
 			},
 		},
 		{