fix(gateway/services): admin node/render pages 500 — redirect loop + is_admin claim

- gateway proxy: trim trailing slash before forwarding upstream. gin's
  RedirectTrailingSlash adds /nodes → /nodes/ while render-svc redirects
  /nodes/ → /nodes, forming an infinite redirect loop (admin pages 500'd)
- accept is_admin as bool OR string "true" in render/file/notification/gateway
  auth middleware (identity emits it as a string) — admin endpoints were 403'ing

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

services/gateway/internal/middleware/auth.go

@@ -75,7 +75,13 @@ func validateAndInject(c *gin.Context, secret string) bool {
 	claims, _ := token.Claims.(jwt.MapClaims)
 	userID, _ := uuid.Parse(fmt.Sprintf("%v", claims["sub"]))
 	tenantID, _ := uuid.Parse(fmt.Sprintf("%v", claims["tenant_id"]))
-	isAdmin, _ := claims["is_admin"].(bool)
+	isAdmin := false
+	switch v := claims["is_admin"].(type) {
+	case bool:
+		isAdmin = v
+	case string:
+		isAdmin = v == "true"
+	}
 	role, _ := claims["role"].(string)
 
 	c.Set(CtxUserID, userID)
@@ -116,7 +122,13 @@ func OptionalJWTAuth(secret string) gin.HandlerFunc {
 		claims, _ := token.Claims.(jwt.MapClaims)
 		userID, _ := uuid.Parse(fmt.Sprintf("%v", claims["sub"]))
 		tenantID, _ := uuid.Parse(fmt.Sprintf("%v", claims["tenant_id"]))
-		isAdmin, _ := claims["is_admin"].(bool)
+		isAdmin := false
+		switch v := claims["is_admin"].(type) {
+		case bool:
+			isAdmin = v
+		case string:
+			isAdmin = v == "true"
+		}
 		c.Request.Header.Set(HeaderUserID, userID.String())
 		c.Request.Header.Set(HeaderTenantID, tenantID.String())
 		if isAdmin {

services/gateway/internal/proxy/proxy.go

@@ -38,6 +38,13 @@ func New(name, target string) *Upstream {
 	orig := rp.Director
 	rp.Director = func(req *http.Request) {
 		orig(req)
+		// Normalise away a trailing slash (gin's RedirectTrailingSlash adds one when a
+		// route is registered as catch-all, e.g. /v1/nodes/*path, but upstream services
+		// register the canonical no-slash form and redirect /nodes/ → /nodes — without
+		// this the two redirects form an infinite loop).
+		if len(req.URL.Path) > 1 && strings.HasSuffix(req.URL.Path, "/") {
+			req.URL.Path = strings.TrimRight(req.URL.Path, "/")
+		}
 		req.Header.Set("X-Forwarded-Host", req.Host)
 		req.Header.Del("X-Forwarded-For") // let httputil re-add it properly
 		req.Host = u.Host