Add AI chat with Ollama tool calling for financial queries

Conversational AI chat that uses Ollama's native tool-calling API to query
transactions, spending reports, account balances, dashboard summaries, and
update transaction categories through natural language. Includes persistent
conversation history, a full-page chat UI with sidebar, and rich inline
rendering of tool results (tables, alerts, cards).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/services/chat.ts

@@ -0,0 +1,16 @@
+import api from './api'
+import type { ChatConversation, ChatConversationDetail, SendChatMessageResponse } from '@/types'
+
+export const chatApi = {
+  sendMessage: (data: { conversationId?: string; message: string }) =>
+    api.post<SendChatMessageResponse>('/chat/send', data),
+
+  getConversations: () =>
+    api.get<ChatConversation[]>('/chat/conversations'),
+
+  getConversation: (id: string) =>
+    api.get<ChatConversationDetail>(`/chat/conversations/${id}`),
+
+  deleteConversation: (id: string) =>
+    api.delete(`/chat/conversations/${id}`),
+}