allow creating a new message with an attachment if it's to an existing chat

[bluebubbles-copilot]

right now we dont allow selecting an attachment until you are physically in the chat. if the chat is existing, we should allow selecting one

Issue Metadata

• User: @zach.shames#0
• Context: https://discord.com/channels/640229510662455326/1251723862228471870/1254109166654455908