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

ratelimit.go

@@ -18,8 +18,9 @@ type RateLimitConfig struct {
 type ActionOption func(*actionEntry)
 
 type actionEntry struct {
-	fn      func()
-	limiter *rate.Limiter // nil = use context default
+	fn         func()
+	limiter    *rate.Limiter // nil = use context default
+	middleware []Middleware
 }
 
 // WithRateLimit returns an ActionOption that gives this action its own