fix: unify tenant context keys and load tenant_id from JWT

backend/internal/api/middleware/auth.go

@@ -13,6 +13,7 @@ import (
 type contextKey string
 
 const UserIDKey contextKey = "userID"
+const TenantIDKey contextKey = "tenantID"
 
 // Auth validates JWT tokens
 func Auth(cfg *config.Config) func(http.Handler) http.Handler {
@@ -46,7 +47,9 @@ func Auth(cfg *config.Config) func(http.Handler) http.Handler {
 			}
 
 			userID := claims["user_id"].(string)
+			tenantID := claims["tenant_id"].(string)
 			ctx := context.WithValue(r.Context(), UserIDKey, userID)
+			ctx = context.WithValue(ctx, TenantIDKey, tenantID)
 			next.ServeHTTP(w, r.WithContext(ctx))
 		})
 	}

backend/internal/api/middleware/tenant.go

@@ -9,10 +9,7 @@ import (
 	"aggios-app/backend/internal/repository"
 )
 
-type tenantContextKey string
-
-const TenantIDKey tenantContextKey = "tenantID"
-const SubdomainKey tenantContextKey = "subdomain"
+const SubdomainKey contextKey = "subdomain"
 
 // TenantDetector detects tenant from subdomain
 func TenantDetector(tenantRepo *repository.TenantRepository) func(http.Handler) http.Handler {