feat(server): add localized agent starter config endpoint

Add a public GET /api/ui/agent-starters endpoint returning localized
empty-state content (title, description, preview images, and starter
prompts) for the canvas Agent panel. Content is server-configurable via
AgentStarter config with built-in zh-CN/en-US fallbacks, and the route is
exempt from authentication so shared canvases render the same content.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

server/internal/handler/get_agent_starter_config_handler.go

@@ -0,0 +1,31 @@
+// Code scaffolded by goctl. Safe to edit.
+// goctl 1.10.1
+
+package handler
+
+import (
+	"net/http"
+
+	"github.com/zeromicro/go-zero/rest/httpx"
+	"img_infinite_canvas/internal/logic"
+	"img_infinite_canvas/internal/svc"
+	"img_infinite_canvas/internal/types"
+)
+
+func getAgentStarterConfigHandler(svcCtx *svc.ServiceContext) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		var req types.GetAgentStarterConfigRequest
+		if err := httpx.Parse(r, &req); err != nil {
+			httpx.ErrorCtx(r.Context(), w, err)
+			return
+		}
+
+		l := logic.NewGetAgentStarterConfigLogic(r.Context(), svcCtx)
+		resp, err := l.GetAgentStarterConfig(&req)
+		if err != nil {
+			httpx.ErrorCtx(r.Context(), w, err)
+		} else {
+			httpx.OkJsonCtx(r.Context(), w, resp)
+		}
+	}
+}

server/internal/handler/routes.go

@@ -329,6 +329,11 @@ func RegisterHandlers(server *rest.Server, serverCtx *svc.ServiceContext) {
 				Path:    "/shares/:shareId",
 				Handler: resolveShareHandler(serverCtx),
 			},
+			{
+				Method:  http.MethodGet,
+				Path:    "/ui/agent-starters",
+				Handler: getAgentStarterConfigHandler(serverCtx),
+			},
 		},
 		rest.WithPrefix("/api"),
 	)

server/internal/handler/user_context_middleware.go

@@ -107,7 +107,8 @@ func requiresAuthenticatedUser(r *http.Request) bool {
 		strings.HasPrefix(path, "/api/shares/") ||
 		path == "/api/auth/options" ||
 		path == "/api/health" ||
-		path == "/api/dashboard" {
+		path == "/api/dashboard" ||
+		path == "/api/ui/agent-starters" {
 		return false
 	}
 	return true

server/internal/handler/user_context_middleware_test.go

@@ -86,6 +86,24 @@ func TestUserContextMiddlewareIgnoresSpoofedUserIDOnPublicRoute(t *testing.T) {
 	}
 }
 
+func TestUserContextMiddlewareAllowsPublicAgentStarterConfig(t *testing.T) {
+	req := httptest.NewRequest(http.MethodGet, "/api/ui/agent-starters?locale=en-US", nil)
+	rec := httptest.NewRecorder()
+
+	called := false
+	UserContextMiddleware(fakeBearerAuthenticator{})(func(w http.ResponseWriter, _ *http.Request) {
+		called = true
+		w.WriteHeader(http.StatusNoContent)
+	})(rec, req)
+
+	if !called {
+		t.Fatal("expected public agent starter config route to continue")
+	}
+	if rec.Code != http.StatusNoContent {
+		t.Fatalf("expected status %d, got %d", http.StatusNoContent, rec.Code)
+	}
+}
+
 func TestUserContextMiddlewareAuthorizesAnonymousCanvasShare(t *testing.T) {
 	ownerID := "d1d2fbbb-97bb-4406-8d0b-ec814cc65092"
 	authorizer := fakeShareAuthorizer{access: sharingmodule.Access{