fix(tui): make opencode theme default

packages/tui/internal/config/config.go

@@ -18,7 +18,7 @@ type State struct {
 
 func NewState() *State {
 	return &State{
-		Theme: "system",
+		Theme: "opencode",
 	}
 }
 

packages/tui/internal/theme/manager.go

@@ -93,14 +93,14 @@ func AvailableThemes() []string {
 		names = append(names, name)
 	}
 	slices.SortFunc(names, func(a, b string) int {
-		if a == "system" {
+		if a == "opencode" {
 			return -1
-		} else if b == "system" {
+		} else if b == "opencode" {
 			return 1
 		}
-		if a == "opencode" {
+		if a == "system" {
 			return -1
-		} else if b == "opencode" {
+		} else if b == "system" {
 			return 1
 		}
 		return strings.Compare(a, b)