Add "New Chat" / "New Session" action to Windows Companion — currently only past conversations are selectable

Summary

The Windows Companion chat UI only lets you select/reopen past conversations from the session list. There is no visible way to start a new chat session or choose which agent a new session should use.

Current behavior

• Sidebar / chat list shows existing sessions only.
• No "+ New Chat" / "New Session" control anywhere in the Chat view.
• To talk to a different agent, or start a clean conversation, there's no obvious path — you're stuck reusing or scrolling through past chats.

Impact

• Can't start a fresh conversation without an existing session to branch from.
• Can't pick/select which agent a new session should target.
• Feels like a missing core action compared to other OpenClaw clients (e.g. web chat), which do support starting a new session + agent picker.

Suggested fix

• Add a "New Chat" button/action (e.g. next to search, or in the Chat sidebar header).
• On new chat creation, allow selecting the target agent (if multiple agents are configured).
• Newly created session should appear in the session list like any other.

Related

• #859 (Improve chat experience — general chat papercuts bucket)
• #1183 (UX for switching chats/sessions isn't super clear)

Environment

• OpenClaw Windows Companion (Chat view)
• Reported 2026-08-30

Start in the Windows Companion Chat view, especially the sidebar or chat list header where existing sessions are shown. Add an obvious new-chat action with agent selection when applicable, and verify that a fresh session appears in the session list and can be opened.