feat(01-02): dispatch typed events with request context

- App-owned festival bus with Fire, Collect and UntilHandled
- Recover listener panics with owner plugin IDs; isolate buses per app
- towel context accessors and hello command demo of all three modes

backpack/app.go

@@ -5,12 +5,14 @@ import (
 	"sync"
 
 	"git.golem15.com/golem15/summercms/compass"
+	"git.golem15.com/golem15/summercms/festival"
 )
 
 // App is the per-instance application container. It must not import party.
 type App struct {
 	Config   *compass.Config
 	Services *Registry
+	Events   *festival.Bus
 
 	mu      sync.RWMutex
 	plugins map[string]struct{}
@@ -21,6 +23,7 @@ func New(cfg *compass.Config) *App {
 	return &App{
 		Config:   cfg,
 		Services: NewRegistry(),
+		Events:   festival.New(),
 		plugins:  make(map[string]struct{}),
 	}
 }