fix: align dot grid to snap grid and fix node selection layout shift

frontend/src/components/canvas/CanvasContainer.tsx

@@ -98,7 +98,7 @@ export function CanvasContainer({ onConnect: onConnectProp, onEdgeDoubleClick, o
       >
         <Background
           variant={BackgroundVariant.Dots}
-          gap={24}
+          gap={16}
           size={1}
           color={theme.colors.canvasDotColor}
         />

frontend/src/components/canvas/nodes/BaseNode.tsx

@@ -39,11 +39,13 @@ export function BaseNode({ id, data, selected, icon: typeIcon, width, height }:
       style={{
         background: colors.background,
         borderColor: colors.border,
-        borderWidth: selected ? 2 : 1,
-        boxShadow: isOnline
+        borderWidth: 1,
+        boxShadow: isOnline && selected
+          ? `0 0 0 1px ${colors.border}, 0 0 10px ${colors.border}2e, 0 0 3px ${colors.border}1a`
+          : isOnline
           ? `0 0 10px ${colors.border}2e, 0 0 3px ${colors.border}1a`
           : selected
-          ? `0 0 8px ${colors.border}44`
+          ? `0 0 0 1px ${colors.border}, 0 0 8px ${colors.border}44`
           : 'none',
         opacity: data.status === 'offline' ? 0.55 : 1,
         minWidth: 140,
@@ -55,7 +57,7 @@ export function BaseNode({ id, data, selected, icon: typeIcon, width, height }:
         isVisible={selected}
         minWidth={140}
         minHeight={50}
-        lineStyle={{ borderColor: colors.border, borderWidth: 1 }}
+        lineStyle={{ borderColor: 'transparent' }}
         handleStyle={{ borderColor: colors.border, background: colors.border, width: 8, height: 8 }}
       />
       <Handle

frontend/src/components/canvas/nodes/GroupRectNode.tsx

@@ -73,7 +73,7 @@ export function GroupRectNode({ id, data, selected }: NodeProps<Node<NodeData>>)
           background: '#00d4ff',
           border: '1px solid #0d1117',
         }}
-        lineStyle={{ borderColor: '#00d4ff55', borderWidth: 1 }}
+        lineStyle={{ borderColor: 'transparent' }}
       />
       <div
         style={{
@@ -86,7 +86,8 @@ export function GroupRectNode({ id, data, selected }: NodeProps<Node<NodeData>>)
           justifyContent: posStyle.justifyContent,
           padding: 12,
           background: backgroundColor,
-          border: `${selected ? borderWidth + 1 : borderWidth}px ${selected ? 'solid' : borderStyle} ${selected ? '#00d4ff' : borderColor}`,
+          border: `${borderWidth}px ${borderStyle} ${borderColor}`,
+          boxShadow: selected ? '0 0 0 1px #00d4ff, 0 0 8px #00d4ff44' : 'none',
           borderRadius: 10,
           boxSizing: 'border-box',
           cursor: 'default',