Make left sidebar resizable

[ComputelessComputer]

Wrap the desktop left sidebar in a persistent resizable panel and cover expanded/collapsed layout states with tests.

---

Note

Low Risk
UI layout change with tests; no auth, data, or API impact. Minor risk of drag-region or chrome misalignment during resize.

Overview
The desktop classic main layout replaces a fixed 200px sidebar with a horizontal resizable panel when the left sidebar is expanded and the user is not on onboarding.

ClassicMainBody wraps sidebar and main content in ResizablePanelGroup with persisted layout (autoSaveId classic-main-sidebar), default 18% width, 12–32% bounds, and 180–360px min/max width. A resize handle appears only in that expanded state; collapsed and onboarding flows keep a single main panel with no handle. Top left sidebar chrome (data-left-sidebar-chrome) now tracks panel size via inline width instead of w-[200px].

LeftSidebar switches from w-[200px] to w-full so it fills the resizable panel. New body.test.tsx covers expanded panel behavior, chrome sync on layout, collapsed layout, and onboarding; shared body.test.tsx expectations update for the resizable root classes.

^{Reviewed by Cursor Bugbot for commit df5d3e9. Bugbot is set up for automated code reviews on this repo. Configure here.}

[netlify]

✅ Deploy Preview for old-char canceled.

Name	Link
🔨 Latest commit	df5d3e9
🔍 Latest deploy log	https://app.netlify.com/projects/old-char/deploys/6a3894377578eb0008ee786f

[cursor]

Cursor Bugbot has reviewed your changes using default effort and found 1 potential issue.

^{❌ Bugbot Autofix is OFF. To automatically fix reported issues with cloud agents, enable autofix in the Cursor dashboard.}

^{Reviewed by Cursor Bugbot for commit 19e9714. Configure here.}