fix: show conversations in collapsed sidebar

[YfengJ]

HUMAN:

Needs human manual UI testing before this checkbox can be checked.

• A human has tested these changes.

AGENT:

I reproduced the code path from issue #1194: SidebarRailBody always passes the collapsed state to SidebarConversationList, but SidebarConversationList returned null when collapsed, removing the conversation picker entirely. This PR routes the collapsed state into the existing compact conversation panel/row UI and adds a regression step to the mock-LLM conversation flow.

---

Why

When the desktop sidebar is collapsed, users should still be able to select an existing conversation without expanding the sidebar first. The current collapsed render path removes the conversation list entirely.

Summary

• Render ConversationPanel in compact mode inside the collapsed sidebar instead of returning null.
• Use the same currently visible conversation set for compact rows, so previous conversations can be selected from the icon rail.
• Add a mock-LLM e2e regression step that collapses the sidebar and resumes an existing conversation through the compact row.

Issue Number

Fixes #1194

How to Test

Agent-run checks:

• npm run lint
• npm run build:app

Manual UI test steps for a reviewer:

1. npm ci
2. npm run dev:mock
3. Create or open an existing conversation.
4. Confirm the expanded sidebar shows the conversation.
5. Collapse the sidebar.
6. Confirm the compact conversation row remains visible and clicking it opens the existing conversation.

Attempted full mock-LLM e2e locally with:
env -u http_proxy -u https_proxy -u all_proxy NO_PROXY=localhost,127.0.0.1,::1 DEBUG=pw:webserver npm run test:e2e:mock-llm -- conversations/mock-llm-conversation.spec.ts

That full-stack local run could not start because the local Python mock-LLM server was missing the openhands SDK module.

Video/Screenshots

Not provided. The compact row behavior is covered by the added e2e regression step, but the local full-stack e2e environment was blocked before the browser flow could start.

Type

• Bug fix
• Feature
• Refactor
• Breaking change
• Docs / chore

Notes

The Vercel preview check currently requires OpenHands team authorization for this forked PR.

[vercel]

@YfengJ is attempting to deploy a commit to the openhands Team on Vercel.

A member of the Team first needs to authorize it.