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/components/layout/AppLayout.vue

@@ -150,6 +150,7 @@ const navItems = [
   { title: 'Loans', icon: 'mdi-home-city', route: '/loans' },
   { title: 'Reports', icon: 'mdi-chart-bar', route: '/reports' },
   { title: 'Investments', icon: 'mdi-finance', route: '/investments' },
+  { title: 'AI Chat', icon: 'mdi-robot-outline', route: '/chat' },
   { title: 'Plugins', icon: 'mdi-puzzle', route: '/plugins' },
   { title: 'Settings', icon: 'mdi-cog', route: '/settings' },
 ]