feat(activity): per-tenant audit feed in notification dropdown

activity_events records booking lifecycle transitions with the actor
behind each change — staff (dashboard), customer (self-service), or
system (auto-promotion). The notification dropdown leads with the real
feed instead of derived recent-booking guesses.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

apps/backend/internal/api/server.go

@@ -11,6 +11,7 @@ import (
 	"strings"
 	"time"
 
+	"bookra/apps/backend/internal/activity"
 	"bookra/apps/backend/internal/admin"
 	"bookra/apps/backend/internal/auth"
 	"bookra/apps/backend/internal/billing"
@@ -57,6 +58,7 @@ func NewServer(cfg config.Config, pools *db.Pools) (*Server, error) {
 	billingService := billing.NewService(cfg, repository)
 	catalogService := catalog.NewService(repository, billingService, notificationService)
 	calendarService := calendar.NewService(repository)
+	activityService := activity.NewService(repository)
 	authService := auth.NewService(repository, cfg.AuthJWTSecret)
 	adminService := admin.NewService(repository, cfg.AdminEmail, cfg.AdminKey)
 	smsService := sms.NewService(cfg, repository)
@@ -1277,6 +1279,20 @@ func NewServer(cfg config.Config, pools *db.Pools) (*Server, error) {
 		c.JSON(http.StatusOK, gin.H{"token": token, "feedPath": "/v1/public/calendar/" + token + ".ics"})
 	})
 
+	protected.GET("/activity", func(c *gin.Context) {
+		limit, _ := strconv.Atoi(c.DefaultQuery("limit", "50"))
+		response, err := activityService.List(c.Request.Context(), auth.PrincipalFromContext(c), limit)
+		if err != nil {
+			status := http.StatusInternalServerError
+			if errors.Is(err, activity.ErrTenantMembership) {
+				status = http.StatusNotFound
+			}
+			c.JSON(status, gin.H{"error": err.Error()})
+			return
+		}
+		c.JSON(http.StatusOK, response)
+	})
+
 	protected.GET("/billing/subscription", func(c *gin.Context) {
 		response, err := billingService.GetSubscription(c.Request.Context(), auth.PrincipalFromContext(c))
 		if err != nil {