fix: align the primary sidebar divider

The primary sidebar resize hit target still reserved four pixels in the flex row, leaving a visible gap between the divider and the content frame. Its opposing negative margins now keep the nine-pixel pointer target layout-neutral while preserving the aligned one-pixel divider.

Release note: 修复主侧栏拖拽分隔线与内容边缘未对齐的问题。

src/renderer/src/AppSidebarLayout.test.ts

@@ -0,0 +1,20 @@
+import { readFileSync } from 'node:fs'
+import { join } from 'node:path'
+import { describe, expect, it } from 'vitest'
+
+const stylesheet = readFileSync(
+  join(process.cwd(), 'src', 'renderer', 'src', 'styles.css'),
+  'utf8'
+).replaceAll('\r\n', '\n')
+
+describe('primary sidebar layout', () => {
+  it('keeps the resize hit target from adding space beside the divider', () => {
+    const rule = stylesheet.match(
+      /\.primary-sidebar-resize-handle\s*\{([^}]*)\}/u
+    )?.[1]
+
+    expect(rule).toContain('width: 9px;')
+    expect(rule).toContain('margin-left: -5px;')
+    expect(rule).toContain('margin-right: -4px;')
+  })
+})

src/renderer/src/styles.css

@@ -2404,6 +2404,7 @@ textarea:focus-visible {
   min-width: 9px;
   padding: 0;
   margin-left: -5px;
+  margin-right: -4px;
   background: transparent;
   cursor: col-resize;
   touch-action: none;