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/ChatInput.tsx

@@ -0,0 +1,85 @@
+/**
+ * Chat Input Component
+ * Textarea with send button. Enter to send, Shift+Enter for new line.
+ */
+import { useState, useRef, useEffect, useCallback } from 'react';
+import { Send, Square } from 'lucide-react';
+import { Button } from '@/components/ui/button';
+import { Textarea } from '@/components/ui/textarea';
+
+interface ChatInputProps {
+  onSend: (text: string) => void;
+  disabled?: boolean;
+  sending?: boolean;
+}
+
+export function ChatInput({ onSend, disabled = false, sending = false }: ChatInputProps) {
+  const [input, setInput] = useState('');
+  const textareaRef = useRef<HTMLTextAreaElement>(null);
+
+  // Auto-resize textarea
+  useEffect(() => {
+    if (textareaRef.current) {
+      textareaRef.current.style.height = 'auto';
+      textareaRef.current.style.height = `${Math.min(textareaRef.current.scrollHeight, 200)}px`;
+    }
+  }, [input]);
+
+  const handleSend = useCallback(() => {
+    const trimmed = input.trim();
+    if (!trimmed || disabled || sending) return;
+    onSend(trimmed);
+    setInput('');
+    // Reset textarea height
+    if (textareaRef.current) {
+      textareaRef.current.style.height = 'auto';
+    }
+  }, [input, disabled, sending, onSend]);
+
+  const handleKeyDown = useCallback(
+    (e: React.KeyboardEvent) => {
+      if (e.key === 'Enter' && !e.shiftKey) {
+        e.preventDefault();
+        handleSend();
+      }
+    },
+    [handleSend],
+  );
+
+  return (
+    <div className="border-t bg-background p-4">
+      <div className="flex items-end gap-2 max-w-4xl mx-auto">
+        <div className="flex-1 relative">
+          <Textarea
+            ref={textareaRef}
+            value={input}
+            onChange={(e) => setInput(e.target.value)}
+            onKeyDown={handleKeyDown}
+            placeholder={disabled ? 'Gateway not connected...' : 'Message (Enter to send, Shift+Enter for new line)'}
+            disabled={disabled}
+            className="min-h-[44px] max-h-[200px] resize-none pr-4"
+            rows={1}
+          />
+        </div>
+
+        <Button
+          onClick={handleSend}
+          disabled={!input.trim() || disabled}
+          size="icon"
+          className="shrink-0 h-10 w-10"
+          variant={sending ? 'destructive' : 'default'}
+        >
+          {sending ? (
+            <Square className="h-4 w-4" />
+          ) : (
+            <Send className="h-4 w-4" />
+          )}
+        </Button>
+      </div>
+
+      <p className="text-xs text-muted-foreground mt-1.5 text-center">
+        Enter to send, Shift+Enter for new line
+      </p>
+    </div>
+  );
+}