feat(canvas): 画布媒体工作流 - 支持批量连线、失败重试与模型能力增强

合并 PR #230。保留当前主线样式与组件结构，吸收批量连线、失败批次重试、媒体模型能力和相关后端增强，并修复集成检查发现的分辨率选择器启用条件与测试稳定性问题。

web/src/components/canvas/canvas-node.tsx

@@ -23,6 +23,7 @@ type CanvasNodeProps = {
     isFocusRelated: boolean;
     isConnectionTarget: boolean;
     isConnecting: boolean;
+    forceInputVisible?: boolean;
     showImageInfo: boolean;
     reduceMediaEffects?: boolean;
     readOnly?: boolean;
@@ -66,6 +67,7 @@ export const CanvasNode = React.memo(function CanvasNode({
     isRelated,
     isFocusRelated,
     isConnectionTarget,
+    forceInputVisible = false,
     showImageInfo,
     reduceMediaEffects = false,
     readOnly = false,
@@ -442,7 +444,7 @@ export const CanvasNode = React.memo(function CanvasNode({
                 </> : null}
             </div>
 
-            {!readOnly && data.type !== CanvasNodeType.Script ? <ConnectionSideRail side="left" scale={scale} visible={hovered} theme={theme} onPointerDown={(event, anchorRatio) => onConnectStart(event, data.id, "target", undefined, anchorRatio)} /> : null}
+            {!readOnly && data.type !== CanvasNodeType.Script ? <ConnectionSideRail side="left" scale={scale} visible={hovered || forceInputVisible} theme={theme} onPointerDown={(event, anchorRatio) => onConnectStart(event, data.id, "target", undefined, anchorRatio)} /> : null}
             {!readOnly && data.type !== CanvasNodeType.Script && data.type !== CanvasNodeType.Config ? <ConnectionSideRail side="right" scale={scale} visible={hovered} theme={theme} onPointerDown={(event, anchorRatio) => onConnectStart(event, data.id, "source", undefined, anchorRatio)} /> : null}
 
         </div>