Fix counter example to use Component return type

- Add (Component) return type to App() and Counter() functions
- Ensures proper component generation with constructors and render methods

Author: claude

examples/counter/app.gx

@@ -2,7 +2,7 @@ package main
 
 import "strconv"
 
-func App() {
+func App() (Component) {
 	counter := make(chan int, 10)
 
 	Div(Class("app-container")) {

examples/counter/counter.gx

@@ -1,6 +1,6 @@
 package main
 
-func Counter(counterChannel chan int) {
+func Counter(counterChannel chan int) (Component) {
     Div(Class("counter-display")) {
         Span(Class("counter-value")) {
             `Counter: {<-counterChannel}`