refactor(web): 前端单页收敛修正——导航式侧边栏 + 去输入模式 chip，mode 由后端自切

按设计/01 §3 + 主人要求：行为模式切换由后端/agent 自切（热切换），前端不再提供
手动切换的行为模式按钮列表。
- 侧边栏改为导航式（连接状态 / 设置 / 管理面板 / 主题），不再列行为模式按钮；
  App.tsx 还原 <Sidebar/> 布局。
- ChatInput 去掉行为模式 chip 切换条（模式不由用户手选）。
- useChat.send/chatStream 不再传 mode；消息 mode 由后端在回复时决定，
  MessageBubble 仍按 message.mode 渲染。
- ChatShell onVoice 为占位（语音处理在 agent）。

frontend/web/src/components/ChatInput.tsx

@@ -1,25 +1,14 @@
 import { useEffect, useRef, useState } from "react";
 import { Button } from "./primitives";
-import { Icon, type IconName } from "./Icon";
-import { useModeStore } from "../store/useModeStore";
-import type { Mode } from "../lib/types";
+import { Icon } from "./Icon";
 
 export interface ChatInputProps {
-  onSend: (text: string, mode: Mode) => void;
+  onSend: (text: string) => void;
   sending: boolean;
   onVoice: () => void;
   placeholder?: string;
 }
 
-const INPUT_MODES: ReadonlyArray<{ mode: Mode; label: string; icon: IconName }> = [
-  { mode: "chat", label: "对话", icon: "chat" },
-  { mode: "code", label: "代码", icon: "terminal" },
-  { mode: "home", label: "家居", icon: "home" },
-  { mode: "work", label: "工作", icon: "folder" },
-  { mode: "docs", label: "知识库", icon: "docs" },
-  { mode: "vision", label: "视觉", icon: "vision" },
-];
-
 export function ChatInput({
   onSend,
   sending,
@@ -28,8 +17,6 @@ export function ChatInput({
 }: ChatInputProps): React.ReactNode {
   const [value, setValue] = useState("");
   const taRef = useRef<HTMLTextAreaElement>(null);
-  const mode = useModeStore((s) => s.mode);
-  const setMode = useModeStore((s) => s.setMode);
 
   // auto-grow the textarea up to a max height
   useEffect(() => {
@@ -42,31 +29,12 @@ export function ChatInput({
   const submit = () => {
     const t = value.trim();
     if (!t || sending) return;
-    onSend(t, mode);
+    onSend(t);
     setValue("");
   };
 
   return (
     <div className="glass sticky bottom-0 border-t border-[var(--mu-glass-border)] p-3 md:p-4">
-      {/* input-mode switcher: sets the mode for the NEXT message (design/07 §1). */}
-      <div className="mx-auto mb-2 flex max-w-2xl items-center gap-1 overflow-x-auto pb-0.5">
-        <span className="mr-1 shrink-0 text-[10px] text-[var(--mu-text-lo)]">行为模式</span>
-        {INPUT_MODES.map(({ mode: m, label, icon }) => (
-          <button
-            key={m}
-            onClick={() => setMode(m)}
-            className={`inline-flex shrink-0 items-center gap-1 rounded-[var(--mu-radius-pill)] px-2.5 py-1 text-xs transition-all duration-200 ease-[var(--mu-spring)] active:scale-95 ${
-              mode === m
-                ? "bg-[var(--mu-accent)]/15 text-[var(--mu-accent-hi)]"
-                : "bg-[var(--mu-surface-4)] text-[var(--mu-text-mid)] hover:bg-[var(--mu-surface-5)]"
-            }`}
-          >
-            <Icon name={icon} size={13} />
-            {label}
-          </button>
-        ))}
-      </div>
-
       <div className="mx-auto flex max-w-2xl items-end gap-2 rounded-[var(--mu-radius-lg)] bg-[var(--mu-surface-2)] p-2 shadow-[var(--mu-shadow-1)]">
         <textarea
           ref={taRef}