feat: add middleware, route groups, and codebase cleanup

* feat: add middleware example demonstrating route groups

Self-contained example covering v.Use(), v.Group(), nested groups,
Group.Use(), and middleware chaining with role-based access control.

* feat: add per-action middleware via WithMiddleware ActionOption

Reuses the existing Middleware type so the same auth/logging functions
work at both page and action level. Middleware runs after CSRF and
rate-limit checks, with full access to session and signals.

* feat: add RedirectView helper and refactor session example to use middleware

RedirectView lets middleware abort and redirect in one step. The session
example now uses an authRequired middleware on a route group instead of
an inline check inside the view.

* fix: remove dead code, fix double Load and extractParams mismatch

- Remove componentRegistry (written, never read)
- Remove unused signal methods: Bytes, Int64, Float
- Remove unreachable nil check in registerCtx
- Simplify injectRouteParams (extractParams already returns fresh map)
- Fix double sync.Map.Load in injectSignals
- Merge Shutdown/shutdown into single method
- Inline currSessionNum
- Fix extractParams: mismatched literal segment now returns nil
- Minor: new(bytes.Buffer), go c.Sync(), genRandID reads 4 bytes

internal/examples/session/main.go

@@ -29,7 +29,17 @@ func main() {
 		SessionManager: sm,
 	})
 
-	// Login page
+	// Auth middleware — redirects unauthenticated users to /login
+	authRequired := func(c *via.Context, next func()) {
+		if c.Session().GetString("username") == "" {
+			c.Session().Set("flash", "Please log in first")
+			c.RedirectView("/login")
+			return
+		}
+		next()
+	}
+
+	// Login page (public)
 	v.Page("/login", func(c *via.Context) {
 		flash := c.Session().PopString("flash")
 		usernameInput := c.Signal("")
@@ -64,8 +74,10 @@ func main() {
 		})
 	})
 
-	// Dashboard page (protected)
-	v.Page("/dashboard", func(c *via.Context) {
+	// Protected pages
+	protected := v.Group("", authRequired)
+
+	protected.Page("/dashboard", func(c *via.Context) {
 		logout := c.Action(func() {
 			c.Session().Set("flash", "Goodbye!")
 			c.Session().Delete("username")
@@ -74,14 +86,6 @@ func main() {
 
 		c.View(func() h.H {
 			username := c.Session().GetString("username")
-
-			// Not logged in? Redirect to login
-			if username == "" {
-				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 != "" {