feat: add cookie-based session support using alexedwards/scs (#1)

- Add Session wrapper with typed getters (GetString, GetInt, GetBool, etc.)
- Add flash message support via Pop methods (PopString, PopInt, etc.)
- Add session utilities: Exists, Keys, ID, Clear, Destroy, RenewToken
- Create default session manager in New() for zero-config usage
- Allow custom session manager via Options.SessionManager
- Wrap mux with scs LoadAndSave middleware in Start()
- Add session example demonstrating login/logout with flash messages

context.go

@@ -2,6 +2,7 @@ package via
 
 import (
 	"bytes"
+	"context"
 	"encoding/json"
 	"fmt"
 	"log"
@@ -29,6 +30,7 @@ type Context struct {
 	signals           *sync.Map
 	mu                sync.RWMutex
 	ctxDisposedChan   chan struct{}
+	reqCtx            context.Context
 }
 
 // View defines the UI rendered by this context.
@@ -360,6 +362,16 @@ func (c *Context) GetPathParam(param string) string {
 	return ""
 }
 
+// Session returns the session for this context.
+// Session data persists across page views for the same browser.
+// Returns a no-op session if no SessionManager is configured.
+func (c *Context) Session() *Session {
+	return &Session{
+		ctx:     c.reqCtx,
+		manager: c.app.sessionManager,
+	}
+}
+
 func newContext(id string, route string, v *V) *Context {
 	if v == nil {
 		log.Fatal("create context failed: app pointer is nil")