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>

src/Purrse.Api/Controllers/ChatController.cs

@@ -0,0 +1,40 @@
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+using Purrse.Core.DTOs;
+using Purrse.Core.Interfaces.Services;
+using System.Security.Claims;
+
+namespace Purrse.Api.Controllers;
+
+[Authorize]
+[ApiController]
+[Route("api/[controller]")]
+public class ChatController : ControllerBase
+{
+    private readonly IChatService _chatService;
+    private Guid UserId => Guid.Parse(User.FindFirstValue(ClaimTypes.NameIdentifier)!);
+
+    public ChatController(IChatService chatService) => _chatService = chatService;
+
+    [HttpPost("send")]
+    public async Task<ActionResult<SendChatMessageResponse>> SendMessage(SendChatMessageRequest request)
+        => Ok(await _chatService.SendMessageAsync(UserId, request));
+
+    [HttpGet("conversations")]
+    public async Task<ActionResult<List<ChatConversationResponse>>> GetConversations()
+        => Ok(await _chatService.GetConversationsAsync(UserId));
+
+    [HttpGet("conversations/{id}")]
+    public async Task<ActionResult<ChatConversationDetailResponse>> GetConversation(Guid id)
+    {
+        var conversation = await _chatService.GetConversationAsync(UserId, id);
+        return conversation == null ? NotFound() : Ok(conversation);
+    }
+
+    [HttpDelete("conversations/{id}")]
+    public async Task<ActionResult> DeleteConversation(Guid id)
+    {
+        await _chatService.DeleteConversationAsync(UserId, id);
+        return NoContent();
+    }
+}