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/message-utils.ts

@@ -0,0 +1,131 @@
+/**
+ * Message content extraction helpers
+ * Ported from OpenClaw's message-extract.ts to handle the various
+ * message content formats returned by the Gateway.
+ */
+import type { RawMessage, ContentBlock } from '@/stores/chat';
+
+/**
+ * Extract displayable text from a message's content field.
+ * Handles both string content and array-of-blocks content.
+ */
+export function extractText(message: RawMessage | unknown): string {
+  if (!message || typeof message !== 'object') return '';
+  const msg = message as Record<string, unknown>;
+  const content = msg.content;
+
+  if (typeof content === 'string') {
+    return content;
+  }
+
+  if (Array.isArray(content)) {
+    const parts: string[] = [];
+    for (const block of content as ContentBlock[]) {
+      if (block.type === 'text' && block.text) {
+        parts.push(block.text);
+      }
+      // tool_result blocks may have nested text
+      if (block.type === 'tool_result' && typeof block.content === 'string') {
+        parts.push(block.content);
+      }
+    }
+    return parts.join('\n\n');
+  }
+
+  // Fallback: try .text field
+  if (typeof msg.text === 'string') {
+    return msg.text;
+  }
+
+  return '';
+}
+
+/**
+ * Extract thinking/reasoning content from a message.
+ * Returns null if no thinking content found.
+ */
+export function extractThinking(message: RawMessage | unknown): string | null {
+  if (!message || typeof message !== 'object') return null;
+  const msg = message as Record<string, unknown>;
+  const content = msg.content;
+
+  if (!Array.isArray(content)) return null;
+
+  const parts: string[] = [];
+  for (const block of content as ContentBlock[]) {
+    if (block.type === 'thinking' && block.thinking) {
+      parts.push(block.thinking);
+    }
+  }
+
+  return parts.length > 0 ? parts.join('\n\n') : null;
+}
+
+/**
+ * Extract image attachments from a message.
+ * Returns array of { mimeType, data } for base64 images.
+ */
+export function extractImages(message: RawMessage | unknown): Array<{ mimeType: string; data: string }> {
+  if (!message || typeof message !== 'object') return [];
+  const msg = message as Record<string, unknown>;
+  const content = msg.content;
+
+  if (!Array.isArray(content)) return [];
+
+  const images: Array<{ mimeType: string; data: string }> = [];
+  for (const block of content as ContentBlock[]) {
+    if (block.type === 'image' && block.source) {
+      const src = block.source;
+      if (src.type === 'base64' && src.media_type && src.data) {
+        images.push({ mimeType: src.media_type, data: src.data });
+      }
+    }
+  }
+
+  return images;
+}
+
+/**
+ * Extract tool use blocks from a message.
+ */
+export function extractToolUse(message: RawMessage | unknown): Array<{ id: string; name: string; input: unknown }> {
+  if (!message || typeof message !== 'object') return [];
+  const msg = message as Record<string, unknown>;
+  const content = msg.content;
+
+  if (!Array.isArray(content)) return [];
+
+  const tools: Array<{ id: string; name: string; input: unknown }> = [];
+  for (const block of content as ContentBlock[]) {
+    if (block.type === 'tool_use' && block.name) {
+      tools.push({
+        id: block.id || '',
+        name: block.name,
+        input: block.input,
+      });
+    }
+  }
+
+  return tools;
+}
+
+/**
+ * Format a Unix timestamp (seconds) to relative time string.
+ */
+export function formatTimestamp(timestamp: unknown): string {
+  if (!timestamp) return '';
+  const ts = typeof timestamp === 'number' ? timestamp : Number(timestamp);
+  if (!ts || isNaN(ts)) return '';
+
+  // OpenClaw timestamps can be in seconds or milliseconds
+  const ms = ts > 1e12 ? ts : ts * 1000;
+  const date = new Date(ms);
+  const now = new Date();
+  const diffMs = now.getTime() - date.getTime();
+
+  if (diffMs < 60000) return 'just now';
+  if (diffMs < 3600000) return `${Math.floor(diffMs / 60000)}m ago`;
+  if (diffMs < 86400000) return `${Math.floor(diffMs / 3600000)}h ago`;
+
+  return date.toLocaleTimeString([], { hour: '2-digit', minute: '2-digit' });
+}