fix(sidebar): remove persistent scrollbar gutter on macOS

[Fldicoahkiin]

Summary

• 修复 macOS 上侧栏右侧始终可见的一条白色 gutter
• 原因：overflowY: scroll 强制始终显示滚动条，叠加 scrollbar-gutter: stable 后变成常驻白条
• 修法：将 overflowY 从 scroll 改为 auto；保留 scrollbar-gutter: stable（macOS overlay 模式下 gutter 宽度为 0，无视觉影响；Windows 上仍可防止内容溢出时的 layout shift，沿用 3bc818e 的修复意图）

触发场景

进入项目编辑模式后内容溢出，退出编辑模式后白条仍保留。修复后 macOS 上无任何状态会看到白条；Windows 行为不变。

Test plan

• macOS：正常模式与编辑模式切换，确认无白条残留
• macOS：内容超出滚动区时滚动条按需出现
• Windows：编辑模式进出无横向 layout shift

Summary by CodeRabbit

• Bug Fixes
  • Sidebar scrollbar now appears only when needed rather than always being visible, improving visual clarity.

[netlify]

✅ Deploy Preview for grand-selkie-225f87 canceled.

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 691a7fac-2128-4e72-9613-14747f325ae3

📥 Commits

Reviewing files that changed from the base of the PR and between 93da2cc and 7a66570.

📒 Files selected for processing (1)

• src/layout/AppSidebar.tsx

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📝 Walkthrough

Walkthrough

A single-line change modifies AppSidebar's main scroll container to display the vertical scrollbar conditionally (only when content overflows) rather than always, by changing overflowY from "scroll" to "auto".

Changes

Sidebar Scrollbar Display

Layer / File(s)	Summary
Conditional scrollbar visibility src/layout/AppSidebar.tsx	The sidebar's vertical overflow property changes from overflowY="scroll" to overflowY="auto", allowing the scrollbar to appear only when content exceeds the container height.

🎯 1 (Trivial) | ⏱️ ~1 minute

🐰 A scroll bar's fate, now conditional—
No longer always shown, but practical.
When content fits, space returns,
A cleaner sidebar, as the design turns!

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately reflects the main change: fixing the persistent scrollbar gutter issue on macOS by switching from overflowY='scroll' to overflowY='auto'.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Drop the stable gutter when hiding idle scrollbars

In classic-scrollbar environments, scrollbar-gutter: stable immediately below this line still reserves scrollbar space for overflow: auto even when the sidebar content does not overflow, so changing only overflowY leaves the persistent blank gutter this fix is meant to remove. This still affects macOS users who have scrollbars set to always show, and other non-overlay scrollbar configurations; remove or conditionally disable the stable gutter when using auto.

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