feat(chat): native React chat page with session selector and streaming

Replace the iframe-based Control UI embed with a native React
implementation that communicates directly with the Gateway via
gateway:rpc IPC calls and chat event streaming.

New components:
- ChatToolbar: session selector dropdown, refresh button, thinking toggle
- ChatMessage: message bubbles with markdown (react-markdown + GFM),
  collapsible thinking blocks, tool use cards, image attachments
- ChatInput: textarea with Enter to send, Shift+Enter for new line
- message-utils: extractText/extractThinking/extractImages/extractToolUse
  ported from OpenClaw's message-extract.ts

Rewritten chat store with:
- Session management (sessions.list, switchSession)
- Proper chat.history loading with raw message preservation
- chat.send with idempotencyKey and run tracking
- Streaming via handleChatEvent (delta/final/error/aborted)
- Thinking toggle (show/hide reasoning blocks)

src/pages/Chat/ChatToolbar.tsx

@@ -0,0 +1,81 @@
+/**
+ * Chat Toolbar
+ * Session selector, refresh, and thinking toggle controls.
+ */
+import { RefreshCw, Brain, ChevronDown } from 'lucide-react';
+import { Button } from '@/components/ui/button';
+import { useChatStore } from '@/stores/chat';
+import { cn } from '@/lib/utils';
+
+export function ChatToolbar() {
+  const sessions = useChatStore((s) => s.sessions);
+  const currentSessionKey = useChatStore((s) => s.currentSessionKey);
+  const switchSession = useChatStore((s) => s.switchSession);
+  const refresh = useChatStore((s) => s.refresh);
+  const loading = useChatStore((s) => s.loading);
+  const showThinking = useChatStore((s) => s.showThinking);
+  const toggleThinking = useChatStore((s) => s.toggleThinking);
+
+  const handleSessionChange = (e: React.ChangeEvent<HTMLSelectElement>) => {
+    switchSession(e.target.value);
+  };
+
+  return (
+    <div className="flex items-center gap-2">
+      {/* Session Selector */}
+      <div className="relative">
+        <select
+          value={currentSessionKey}
+          onChange={handleSessionChange}
+          className={cn(
+            'appearance-none rounded-md border border-border bg-background px-3 py-1.5 pr-8',
+            'text-sm text-foreground cursor-pointer',
+            'focus:outline-none focus:ring-2 focus:ring-ring',
+          )}
+        >
+          {/* Always show current session */}
+          <option value={currentSessionKey}>
+            {sessions.find((s) => s.key === currentSessionKey)?.displayName
+              || sessions.find((s) => s.key === currentSessionKey)?.label
+              || currentSessionKey}
+          </option>
+          {/* Other sessions */}
+          {sessions
+            .filter((s) => s.key !== currentSessionKey)
+            .map((s) => (
+              <option key={s.key} value={s.key}>
+                {s.displayName || s.label || s.key}
+              </option>
+            ))}
+        </select>
+        <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>
+
+      {/* Refresh */}
+      <Button
+        variant="ghost"
+        size="icon"
+        className="h-8 w-8"
+        onClick={() => refresh()}
+        disabled={loading}
+        title="Refresh chat"
+      >
+        <RefreshCw className={cn('h-4 w-4', loading && 'animate-spin')} />
+      </Button>
+
+      {/* Thinking Toggle */}
+      <Button
+        variant="ghost"
+        size="icon"
+        className={cn(
+          'h-8 w-8',
+          showThinking && 'bg-primary/10 text-primary',
+        )}
+        onClick={toggleThinking}
+        title={showThinking ? 'Hide thinking' : 'Show thinking'}
+      >
+        <Brain className="h-4 w-4" />
+      </Button>
+    </div>
+  );
+}