fix: persist toolCalls to database for reload persistence

Tool usage was not showing after page reload because the toolCalls
field was not being included when saving assistant messages to the
database. Now toolCalls are properly persisted and restored.

frontend/src/lib/components/chat/ChatWindow.svelte

@@ -604,12 +604,16 @@
 				// The results are stored in toolCalls and displayed by ToolCallDisplay
 			}
 
-			// Persist the assistant message (without flooding text content)
+			// Persist the assistant message (including toolCalls for reload persistence)
 			if (conversationId && assistantNode) {
 				const parentOfAssistant = assistantNode.parentId;
 				await addStoredMessage(
 					conversationId,
-					{ role: 'assistant', content: assistantNode.message.content },
+					{
+						role: 'assistant',
+						content: assistantNode.message.content,
+						toolCalls: assistantNode.message.toolCalls
+					},
 					parentOfAssistant,
 					assistantMessageId
 				);