fix(desktop): hide collapsed sidebar icon rail

[ButterBright]

Summary

Fixes the macOS traffic-light buttons so they no longer span the sidebar and main content area.

When collapsed, the sidebar now:

• Closes completely instead of leaving a 48px icon rail.
• Removes hidden sidebar controls from pointer and keyboard interaction.
• Keeps the titlebar restore action visible so the sidebar can be reopened.

Verification

Added Playwright coverage confirming that:

• The collapsed sidebar has a width of 0px.
• Sidebar navigation is hidden while collapsed.
• The titlebar restore action remains visible.
• The sidebar can be expanded again.

AI use

Select exactly one:

• No generative tool made a substantive contribution
• Generative tooling made a substantive contribution

Tool(s) and scope:

Investigated the collapsed-sidebar layout, implemented the CSS and Storybook updates, added targeted Playwright coverage.

Checklist

• Tests cover the change and fail without it
• Lint, format, typecheck and the affected suites pass locally

Does this PR entail a change in behavior?

• Yes — described under Summary above
• No

[Astro-Han]

Update on 1ffbc27c87:

Standards NO-GO (5 hard): missing real-window smoke (smoke:real-window), incomplete before/after evidence, missing AI-use declaration, incomplete PR template/branch naming. Code itself is Spec PASS — collapsed rail correctly hidden via visibility:hidden with restore action. CI test is still QUEUED — not green.

简体中文

因流程与验证材料缺失暂不通过。

[ButterBright]

Updated.

[Astro-Han]

Thanks, nice fix~ The e2e might need some fix since it changes the folding action. Can we take a look at the e2e test and fix these?