feat(api): add Lovart-style project and agent thread endpoints

Add canva/canda-compatible routes for lightweight project open/save and
agent thread history:
- POST /canva/project/queryProject, saveProject
- POST /canva/agent/queryAgentLastThread, agentThreadList
- GET /canda/chat-history, /canda/thread/status

Canvas save now accepts a compressed SHAKKERDATA:// snapshot payload,
preserves connections, and returns a SaveProject response; blank
successful image nodes are backfilled from generated artifacts. Frontend
designGateway adopts the new save/query flow.

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

frontend/src/infrastructure/authGateway.ts

@@ -1,5 +1,4 @@
 import type { AccountDevice, AuthCodeResponse, AuthOptions, AuthSession, AuthUser, StoredAuthSession } from "@/domain/auth";
-import { encodeUploadImage } from "@/infrastructure/imageUploadEncoding";
 import { createApiFailure, createNetworkFailure } from "@/infrastructure/userMessages";
 
 const sessionStorageKey = "img-infinite-canvas.auth.session";
@@ -116,7 +115,6 @@ export const authGateway = {
   },
 
   async uploadAvatar(file: File) {
-    const uploadFile = await encodeUploadImage(file);
     const upload = await apiRequest<{
       uploadUrl: string;
       publicUrl: string;
@@ -124,9 +122,9 @@ export const authGateway = {
     }>("/api/assets/upload-url", {
       method: "POST",
       body: JSON.stringify({
-        fileName: uploadFile.name,
-        contentType: uploadFile.type || file.type || "application/octet-stream",
-        size: uploadFile.size
+        fileName: file.name,
+        contentType: file.type || "application/octet-stream",
+        size: file.size
       })
     });
 
@@ -134,7 +132,7 @@ export const authGateway = {
       await fetch(upload.uploadUrl, {
         method: "PUT",
         headers: upload.headers,
-        body: uploadFile
+        body: file
       });
     }
     return upload.publicUrl;