fix(web): 本地优先保存与 design 页体验修复

- 保存先写本地缓存，登录后可选云端同步；退出登录不再因文件操作跳转登录

- 修复 Layui 遮罩残留、design2 保存后线条、toast 被 finally 提前关闭

- 保存过程恢复 loading spinner；成功提示 2.5 秒

- 云端 payload 瘦身与体积超限提示；后端 schema 迁移与 FileService 容错

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend-web/js/design2/ui.js

@@ -365,8 +365,6 @@ $('#version_change').click(function () {
         if (typeof window.soonDesign2ScaleBgSources === 'function') {
             window.soonDesign2ScaleBgSources()
         }
-        canvas1.requestRenderAll()
-        canvas2.requestRenderAll()
     }
     sf.onerror = sf.onload
     sf.src = soonAsset('front_bg' + bg_version + '_2.png')
@@ -2703,42 +2701,10 @@ if (typeof window._design2CanvasEventsInitialized === 'undefined') {
     // - mouse:up (已在 core.js 中处理)
     // 如果需要 canvas1 特定的处理逻辑，请修改 core.js 中的相应函数
 
-    // 保留 canvas1 特定的 after:render 处理
-    canvas1.on('after:render', function () {
-        if (!window.is_bgi_add) return
-        var image = document.getElementById('source_front')
-        var metrics = typeof window.soonDesign2BgOverlayMetrics === 'function'
-            ? window.soonDesign2BgOverlayMetrics(image)
-            : null
-        if (!metrics) return
-        ctx1.drawImage(
-            image,
-            (canvas1.width - metrics.w) / 2,
-            (canvas1.height - metrics.h) / 2,
-            metrics.w,
-            metrics.h
-        )
-    })
     // 保留 canvas1 特定的 text:changed 处理
     canvas1.on('text:changed', (e) => {
         $('#text_text').val(e.target.get('text'))
     })
-    // 保留 canvas2 特定的 after:render 处理
-    canvas2.on('after:render', function () {
-        if (!window.is_bgi_add) return
-        var image = document.getElementById('source_back')
-        var metrics = typeof window.soonDesign2BgOverlayMetrics === 'function'
-            ? window.soonDesign2BgOverlayMetrics(image)
-            : null
-        if (!metrics) return
-        ctx2.drawImage(
-            image,
-            (canvas2.width - metrics.w) / 2,
-            (canvas2.height - metrics.h) / 2,
-            metrics.w,
-            metrics.h
-        )
-    })
     requestAnimationFrame(function () {
         requestAnimationFrame(function () {
             if (typeof window.soonDesign2Kickoff === 'function') {