After opening CopilotChat, then typing gh (help) or gc (info) and closing it with q, the q keymap is not cleaned up. Pressing q a second time triggers an E5108 Lua error due to an attempt to restore a buffer to an already-invalid window.

To Reproduce

1. Open CopilotChat (e.g. :CopilotChat)
2. Press gh to show help, or gc to show info
3. Press q to close CopilotChat
4. Press q again

Expected behavior

The q keymap should be removed once the CopilotChat window is closed. Pressing q afterwards should have no effect or fall through to the default Neovim behavior.

Actual behavior

An error is thrown:

E5108: Error executing lua: ...vim/lazy/CopilotChat.nvim/lua/CopilotChat/ui/overlay.lua:119: Invalid 'window': Expected Lua number
stack traceback:
    [C]: in function 'nvim_win_set_buf'
    ...vim/lazy/CopilotChat.nvim/lua/CopilotChat/ui/overlay.lua:119: in function 'restore'
    ...e/nvim/lazy/CopilotChat.nvim/lua/CopilotChat/ui/chat.lua:163: in function <...e/nvim/lazy/CopilotChat.nvim/lua/CopilotChat/ui/chat.lua:162>

Running :map q after closing the window confirms the stale mapping is still active:

n  q     * <Lua 298: ~/.local/share/nvim/lazy/CopilotChat.nvim/lua/CopilotChat/ui/chat.lua:162>

Environment

• NVIM v0.11.6, Build type: RelWithDebInfo, LuaJIT 2.1.1772619647
• OS: macOS and Linux (reproduced on both)
• Plugin: CopilotChat.nvim (via lazy.nvim)