feat(canvas): 画布工作区 - 整合侧栏与风格预设并修复提示词回填

选择性整合 #547，保留主分支节点与工具条设计。新增默认折叠的节点、资产、任务和历史面板，风格与预设保留在节点内，移除重复入口。

补齐工具权限、提示词解析、资源引用保护及数据库迁移，修复提示词清空和连续编辑后的生成配置同步。

验证：前端全量 1925 项测试、构建、类型检查及 lint 通过；后端 go test ./... 通过。真实模型、PostgreSQL 实库与登录态页面验收仍待进行。

Refs #547

Co-authored-by: bensharp <bensharp@qq.com>

web/src/pages/canvas/shared.tsx

@@ -282,7 +282,7 @@ export default function SharedCanvasPage() {
                 }} onHoverStart={keepToolbar} onHoverEnd={hideToolbar} onConnectStart={unauthorized} onResize={() => undefined} onContentChange={unauthorized} onRetry={unauthorized} onOpenTaskDetails={unauthorized} onViewImage={(target) => setInfoNodeId(target.id)} onContextMenu={(event, nodeId) => openContextMenu(event, nodeId)} />)}
             </InfiniteCanvas>
 
-            <CanvasNodeToolbar node={dragRef.current ? null : toolbarNode} viewport={viewport} containerRef={containerRef} onKeep={keepToolbar} onLeave={hideToolbar} onInfo={(node) => setInfoNodeId(node.id)} onEditText={unauthorized} onDecreaseFont={unauthorized} onIncreaseFont={unauthorized} onToggleDialog={unauthorized} onAnnotate={unauthorized} onAnnotationEdit={unauthorized} onTextEdit={unauthorized} onGenerateImage={unauthorized} onUpload={unauthorized} onDownload={unauthorized} onSaveAsset={unauthorized} onMaskEdit={unauthorized} onRemoveBackground={unauthorized} onLayerDecomposition={unauthorized} onEmotion={unauthorized} onPortraitTexture={unauthorized} onCrop={unauthorized} onSplit={unauthorized} onUpscale={unauthorized} onSuperResolve={unauthorized} onAngle={unauthorized} onLighting={unauthorized} onPanorama={unauthorized} onViewImage={unauthorized} onExtractVideoFrames={unauthorized} onExtractAudioFromVideo={unauthorized} onTrimVideoSegments={unauthorized} extractingVideoFrames={false} extractingAudio={false} trimmingVideo={false} onSubtitles={unauthorized} onTimeline={unauthorized} onReversePrompt={unauthorized} onRetry={unauthorized} onToggleFreeResize={unauthorized} onToggleLocked={unauthorized} onDelete={unauthorized} />
+            <CanvasNodeToolbar node={dragRef.current ? null : toolbarNode} viewport={viewport} containerRef={containerRef} onKeep={keepToolbar} onLeave={hideToolbar} onInfo={(node) => setInfoNodeId(node.id)} onEditText={unauthorized} onDecreaseFont={unauthorized} onIncreaseFont={unauthorized} onToggleDialog={unauthorized} onAnnotate={unauthorized} onAnnotationEdit={unauthorized} onTextEdit={unauthorized} onGenerateImage={unauthorized} onUpload={unauthorized} onDownload={unauthorized} onSaveAsset={unauthorized} onMaskEdit={unauthorized} onRemoveBackground={unauthorized} onLayerDecomposition={unauthorized} onEmotion={unauthorized} onPortraitTexture={unauthorized} onCrop={unauthorized} onSplit={unauthorized} onUpscale={unauthorized} onSuperResolve={unauthorized} onAngle={unauthorized} onLighting={unauthorized} onPanorama={unauthorized} onViewImage={unauthorized} onExtractVideoFrames={unauthorized} onExtractAudioFromVideo={unauthorized} onTrimVideoSegments={unauthorized} extractingVideoFrames={false} extractingAudio={false} trimmingVideo={false} onSubtitles={unauthorized} onTimeline={unauthorized} onReversePrompt={unauthorized} onRetry={unauthorized} onToggleFreeResize={unauthorized} onToggleLocked={unauthorized} onDelete={unauthorized} onNineGrid={unauthorized} />
 
             <div className="absolute bottom-5 left-5 z-[var(--z-panel-floating)]"><CanvasZoomControls scale={viewport.k} containerRef={containerRef} onScaleChange={setZoom} onFitContent={resetViewport} isMiniMapOpen={false} onToggleMiniMap={unauthorized} onOpenShortcuts={unauthorized} /></div>
             <div className="pointer-events-none absolute bottom-5 right-5 z-[var(--z-panel-floating)] max-w-[340px] text-right text-xs leading-5" style={{ color: theme.node.muted }}>访客操作仅在当前页面临时生效</div>