feat: add Redirect and ReplaceURL methods for browser navigation

Add SSE-based navigation methods to Context:
- Redirect(url) / Redirectf() - navigate to new page
- ReplaceURL(url) / ReplaceURLf() - update URL without navigation

Update session example to demonstrate full login flow with redirects.

internal/examples/session/main.go

@@ -7,11 +7,11 @@ import (
 
 func main() {
 	v := via.New()
+	v.Config(via.Options{ServerAddress: ":7331"})
 
-	v.Page("/", func(c *via.Context) {
-		username := c.Session().GetString("username")
+	// Login page
+	v.Page("/login", func(c *via.Context) {
 		flash := c.Session().PopString("flash")
-
 		usernameInput := c.Signal("")
 
 		login := c.Action(func() {
@@ -20,38 +20,69 @@ func main() {
 				c.Session().Set("username", name)
 				c.Session().Set("flash", "Welcome, "+name+"!")
 				c.Session().RenewToken()
+				c.Redirect("/dashboard")
 			}
-			c.Sync()
-		})
-
-		logout := c.Action(func() {
-			c.Session().Set("flash", "Goodbye!")
-			c.Session().Delete("username")
-			c.Sync()
 		})
 
 		c.View(func() h.H {
+			// Already logged in? Redirect to dashboard
+			if c.Session().GetString("username") != "" {
+				c.Redirect("/dashboard")
+				return h.Div()
+			}
+
 			var flashMsg h.H
 			if flash != "" {
 				flashMsg = h.P(h.Text(flash), h.Style("color: green"))
 			}
+			return h.Div(
+				flashMsg,
+				h.H1(h.Text("Login")),
+				h.Input(h.Type("text"), h.Placeholder("Username"), usernameInput.Bind()),
+				h.Button(h.Text("Login"), login.OnClick()),
+			)
+		})
+	})
 
+	// Dashboard page (protected)
+	v.Page("/dashboard", func(c *via.Context) {
+		logout := c.Action(func() {
+			c.Session().Set("flash", "Goodbye!")
+			c.Session().Delete("username")
+			c.Redirect("/login")
+		})
+
+		c.View(func() h.H {
+			username := c.Session().GetString("username")
+
+			// Not logged in? Redirect to login
 			if username == "" {
-				return h.Div(
-					flashMsg,
-					h.H1(h.Text("Login")),
-					h.Input(h.Type("text"), h.Placeholder("Username"), usernameInput.Bind()),
-					h.Button(h.Text("Login"), login.OnClick()),
-				)
+				c.Session().Set("flash", "Please log in first")
+				c.Redirect("/login")
+				return h.Div()
+			}
+
+			flash := c.Session().PopString("flash")
+			var flashMsg h.H
+			if flash != "" {
+				flashMsg = h.P(h.Text(flash), h.Style("color: green"))
 			}
 			return h.Div(
 				flashMsg,
-				h.H1(h.Textf("Hello, %s!", username)),
+				h.H1(h.Textf("Dashboard - Hello, %s!", username)),
 				h.P(h.Text("Your session persists across page refreshes.")),
 				h.Button(h.Text("Logout"), logout.OnClick()),
 			)
 		})
 	})
 
+	// Redirect root to login
+	v.Page("/", func(c *via.Context) {
+		c.View(func() h.H {
+			c.Redirect("/login")
+			return h.Div()
+		})
+	})
+
 	v.Start()
 }