fix(chat): move toolbar to Header and add New Session button

- Move ChatToolbar (session selector, refresh, thinking toggle) from
  the Chat page body into the Header component, so controls appear
  at the same level as the "Chat" title
- Add New Session button (+) to create a fresh conversation
- Add newSession action to chat store
- Header conditionally renders ChatToolbar only on /chat route
- Chat page fills full content area without duplicate toolbar

src/components/layout/Header.tsx

@@ -1,8 +1,10 @@
 /**
  * Header Component
- * Top navigation bar with page title
+ * Top navigation bar with page title and page-specific controls.
+ * On the Chat page, shows session selector, refresh, thinking toggle, and new session.
  */
 import { useLocation } from 'react-router-dom';
+import { ChatToolbar } from '@/pages/Chat/ChatToolbar';
 
 // Page titles mapping
 const pageTitles: Record<string, string> = {
@@ -16,13 +18,15 @@ const pageTitles: Record<string, string> = {
 
 export function Header() {
   const location = useLocation();
-  
-  // Get current page title
   const currentTitle = pageTitles[location.pathname] || 'ClawX';
+  const isChatPage = location.pathname === '/chat';
 
   return (
-    <header className="flex h-14 items-center border-b bg-background px-6">
+    <header className="flex h-14 items-center justify-between border-b bg-background px-6">
       <h2 className="text-lg font-semibold">{currentTitle}</h2>
+      
+      {/* Chat-specific controls */}
+      {isChatPage && <ChatToolbar />}
     </header>
   );
 }

src/pages/Chat/ChatToolbar.tsx

@@ -1,8 +1,9 @@
 /**
  * Chat Toolbar
- * Session selector, refresh, and thinking toggle controls.
+ * Session selector, new session, refresh, and thinking toggle.
+ * Rendered in the Header when on the Chat page.
  */
-import { RefreshCw, Brain, ChevronDown } from 'lucide-react';
+import { RefreshCw, Brain, ChevronDown, Plus } from 'lucide-react';
 import { Button } from '@/components/ui/button';
 import { useChatStore } from '@/stores/chat';
 import { cn } from '@/lib/utils';
@@ -11,6 +12,7 @@ export function ChatToolbar() {
   const sessions = useChatStore((s) => s.sessions);
   const currentSessionKey = useChatStore((s) => s.currentSessionKey);
   const switchSession = useChatStore((s) => s.switchSession);
+  const newSession = useChatStore((s) => s.newSession);
   const refresh = useChatStore((s) => s.refresh);
   const loading = useChatStore((s) => s.loading);
   const showThinking = useChatStore((s) => s.showThinking);
@@ -51,6 +53,17 @@ export function ChatToolbar() {
         <ChevronDown className="absolute right-2 top-1/2 -translate-y-1/2 h-3.5 w-3.5 text-muted-foreground pointer-events-none" />
       </div>
 
+      {/* New Session */}
+      <Button
+        variant="ghost"
+        size="icon"
+        className="h-8 w-8"
+        onClick={newSession}
+        title="New session"
+      >
+        <Plus className="h-4 w-4" />
+      </Button>
+
       {/* Refresh */}
       <Button
         variant="ghost"

src/pages/Chat/index.tsx

@@ -10,7 +10,6 @@ import { Card, CardContent } from '@/components/ui/card';
 import { useChatStore } from '@/stores/chat';
 import { useGatewayStore } from '@/stores/gateway';
 import { LoadingSpinner } from '@/components/common/LoadingSpinner';
-import { ChatToolbar } from './ChatToolbar';
 import { ChatMessage } from './ChatMessage';
 import { ChatInput } from './ChatInput';
 import { extractText } from './message-utils';
@@ -63,13 +62,7 @@ export function Chat() {
   const streamText = streamingMessage ? extractText(streamingMessage) : '';
 
   return (
-    <div className="flex h-[calc(100vh-4rem)] flex-col">
-      {/* Toolbar: session selector, refresh, thinking toggle */}
-      <div className="flex items-center justify-between px-4 py-2 border-b">
-        <div /> {/* spacer */}
-        <ChatToolbar />
-      </div>
-
+    <div className="flex flex-col -m-6" style={{ height: 'calc(100vh - 3.5rem)' }}>
       {/* Messages Area */}
       <div className="flex-1 overflow-y-auto px-4 py-4">
         <div className="max-w-4xl mx-auto space-y-4">

src/stores/chat.ts

@@ -60,6 +60,7 @@ interface ChatState {
   // Actions
   loadSessions: () => Promise<void>;
   switchSession: (key: string) => void;
+  newSession: () => void;
   loadHistory: () => Promise<void>;
   sendMessage: (text: string) => Promise<void>;
   handleChatEvent: (event: Record<string, unknown>) => void;
@@ -129,6 +130,23 @@ export const useChatStore = create<ChatState>((set, get) => ({
     get().loadHistory();
   },
 
+  // ── New session ──
+
+  newSession: () => {
+    // Generate a new unique session key and switch to it
+    const newKey = `session-${Date.now()}`;
+    set({
+      currentSessionKey: newKey,
+      messages: [],
+      streamingText: '',
+      streamingMessage: null,
+      activeRunId: null,
+      error: null,
+    });
+    // Reload sessions list to include the new one after first message
+    get().loadSessions();
+  },
+
   // ── Load chat history ──
 
   loadHistory: async () => {