fix(report): prevent sidebar jitter when expanding case selector (#1344)

Fixed sidebar shifting 1-2 pixels when clicking to expand the
playwright case selector. The issue was caused by adding a border
only in the expanded state, causing a sudden height change.

Solution: Added transparent border to the collapsed state, ensuring
consistent height across both states.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude <noreply@anthropic.com>

Author: quanru

apps/report/src/components/playwright-case-selector/index.less

@@ -7,6 +7,7 @@
     padding: 0 12px;
     background: #F2F4F7;
     border-radius: 8px;
+    border: 1px solid transparent;
     cursor: pointer;
     display: flex;
     align-items: center;