fix: chat window UX, settings tabs, and unfocus visibility

[liukewia]

Summary

• Chat window starts at 400px and stays resizable: no height snap on new conversation or first send, resize stays bottom-anchored, empty compact state fills the window.
• Empty chat shows a gray logo that scales with the message area; agent picker matches the model popover, and both grow with a tall window.
• Settings are split into 常规 / 窗口 / 快捷键 / 关于. New option keeps chat and settings visible when clicking another app (on by default). Close buttons follow the OS (macOS traffic-light with hover ×).
• Auth and errors: save logs in and stores the token; silent login with the saved password; HTTP errors show the server message; connection failures offer retry.

Test plan

• Open chat from the pet: window is ~400px, resizable from the bottom-right; sending a message does not snap height
• Empty conversation shows the gray logo; shrink the window and confirm the logo shrinks; expand and confirm it stays modest
• Open agent and model menus in a tall window — lists use remaining height and stay inside the chat card
• Settings: switch 常规 / 窗口 / 快捷键 / 关于; toggle「点击其他应用时保持窗口显示」on/off and click another app
• macOS: hover the close traffic light for ×; Windows/Linux: × on the right
• Save settings with valid credentials; quit/reopen chat with a missing token and confirm silent login
• Force a connection failure and confirm retry; queue a follow-up while streaming and confirm the finished reply is not marked disconnected
• make all

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