Implement AI

API/ROLAC.API/Controllers/ExpenseAiController.cs

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+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+using ROLAC.API.DTOs.Expense;
+using ROLAC.API.Services.Ai;
+
+namespace ROLAC.API.Controllers;
+
+[ApiController]
+[Route("api/expense-ai")]
+[Authorize]   // Open to any authenticated user — same audience as the expense-entry form, which any
+              // member filing a reimbursement can reach. The endpoint only reads the category catalog.
+public class ExpenseAiController : ControllerBase
+{
+    private readonly IExpenseAiService _svc;
+    public ExpenseAiController(IExpenseAiService svc) => _svc = svc;
+
+    [HttpPost("assist")]
+    public async Task<IActionResult> Assist([FromBody] ExpenseAiAssistRequest request, CancellationToken ct)
+    {
+        if (string.IsNullOrWhiteSpace(request.Text))
+            return BadRequest("Text is required.");
+
+        var suggestion = await _svc.SuggestAsync(request.Text, request.Amount, ct);
+        return Ok(suggestion);
+    }
+}