feat(api): .NET 10 multi-tenant REST API

Full backend implementation:
- Multi-tenant cafe/restaurant management (menus, orders, tables, staff)
- POS order flow with ZarinPal and Snappfood payment integration
- OTP authentication via Kavenegar SMS
- QR digital menu with public discover/finder endpoints
- Customer loyalty, coupons, CRM
- PostgreSQL via EF Core, Redis for caching/sessions
- Background jobs, webhook handlers
- Full migration history

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/Meezi.API/Services/CoffeeAdvisorService.cs

@@ -0,0 +1,130 @@
+using System.Text.Json;
+using Microsoft.EntityFrameworkCore;
+using Meezi.API.Models.Public;
+using Meezi.Infrastructure.Data;
+
+namespace Meezi.API.Services;
+
+public interface ICoffeeAdvisorService
+{
+    Task<(CoffeeAdvisorResultDto? Data, string? ErrorCode, string? Message)> RecommendAsync(
+        CoffeeAdvisorRequest request,
+        CancellationToken cancellationToken = default);
+}
+
+public class CoffeeAdvisorService : ICoffeeAdvisorService
+{
+    private static readonly JsonSerializerOptions JsonOpts = new() { PropertyNameCaseInsensitive = true };
+
+    private readonly AppDbContext _db;
+    private readonly IOpenAiChatService _openAi;
+    private readonly ILogger<CoffeeAdvisorService> _logger;
+
+    public CoffeeAdvisorService(
+        AppDbContext db,
+        IOpenAiChatService openAi,
+        ILogger<CoffeeAdvisorService> logger)
+    {
+        _db = db;
+        _openAi = openAi;
+        _logger = logger;
+    }
+
+    public async Task<(CoffeeAdvisorResultDto? Data, string? ErrorCode, string? Message)> RecommendAsync(
+        CoffeeAdvisorRequest request,
+        CancellationToken cancellationToken = default)
+    {
+        var purpose = request.Purpose?.Trim();
+        if (string.IsNullOrWhiteSpace(purpose) || purpose.Length < 3)
+            return (null, "INVALID_REQUEST", "Describe what you need (at least 3 characters).");
+
+        if (!await _openAi.IsConfiguredForCoffeeAdvisorAsync(cancellationToken))
+            return (null, "AI_NOT_CONFIGURED", "Coffee advisor is not available right now.");
+
+        var menuLines = await LoadMenuContextAsync(request.CafeSlug, cancellationToken);
+        var systemPrompt =
+            """
+            You are a specialty coffee advisor for Iranian cafés. Respond ONLY with valid JSON (no markdown).
+            Schema: { "summary": string (1-2 sentences in Persian), "picks": [ { "name": string, "reason": string (Persian), "menuItemId": string|null } ] }
+            Rules: suggest 1-3 drinks; prefer items from the menu list when provided; match the guest's purpose (energy, relax, meeting, dessert pairing, etc.); be concise and friendly in Persian.
+            """;
+        var userPrompt = $"""
+            Guest purpose: {purpose}
+            {(menuLines.Count > 0 ? "Café menu (id | name | description):\n" + string.Join("\n", menuLines) : "No specific café menu — suggest classic café drinks.")}
+            """;
+
+        string? json;
+        try
+        {
+            json = await _openAi.CompleteJsonAsync(systemPrompt, userPrompt, cancellationToken);
+        }
+        catch (Exception ex)
+        {
+            _logger.LogWarning(ex, "Coffee advisor OpenAI call failed");
+            return (null, "AI_FAILED", "Could not get a recommendation. Try again later.");
+        }
+
+        if (string.IsNullOrWhiteSpace(json))
+            return (null, "AI_FAILED", "Could not get a recommendation. Try again later.");
+
+        try
+        {
+            var parsed = JsonSerializer.Deserialize<AdvisorJson>(json, JsonOpts);
+            if (parsed is null || string.IsNullOrWhiteSpace(parsed.Summary))
+                return (null, "AI_FAILED", "Invalid advisor response.");
+
+            var picks = (parsed.Picks ?? [])
+                .Where(p => !string.IsNullOrWhiteSpace(p.Name))
+                .Take(3)
+                .Select(p => new CoffeeAdvisorPickDto(
+                    p.Name!.Trim(),
+                    p.Reason?.Trim() ?? "",
+                    string.IsNullOrWhiteSpace(p.MenuItemId) ? null : p.MenuItemId.Trim()))
+                .ToList();
+
+            return (new CoffeeAdvisorResultDto(parsed.Summary.Trim(), picks), null, null);
+        }
+        catch (JsonException ex)
+        {
+            _logger.LogWarning(ex, "Coffee advisor JSON parse failed");
+            return (null, "AI_FAILED", "Could not parse advisor response.");
+        }
+    }
+
+    private async Task<IReadOnlyList<string>> LoadMenuContextAsync(string? slug, CancellationToken cancellationToken)
+    {
+        if (string.IsNullOrWhiteSpace(slug))
+            return [];
+
+        var cafeId = await _db.Cafes.AsNoTracking()
+            .Where(c => c.Slug == slug.Trim() && c.DeletedAt == null)
+            .Select(c => c.Id)
+            .FirstOrDefaultAsync(cancellationToken);
+        if (cafeId is null)
+            return [];
+
+        var items = await _db.MenuItems.AsNoTracking()
+            .Where(i => i.CafeId == cafeId && i.IsAvailable && i.DeletedAt == null)
+            .OrderBy(i => i.Name)
+            .Take(40)
+            .Select(i => new { i.Id, i.Name, i.Description })
+            .ToListAsync(cancellationToken);
+
+        return items
+            .Select(i => $"{i.Id} | {i.Name} | {(string.IsNullOrWhiteSpace(i.Description) ? "-" : i.Description)}")
+            .ToList();
+    }
+
+    private sealed class AdvisorJson
+    {
+        public string? Summary { get; set; }
+        public List<AdvisorPickJson>? Picks { get; set; }
+    }
+
+    private sealed class AdvisorPickJson
+    {
+        public string? Name { get; set; }
+        public string? Reason { get; set; }
+        public string? MenuItemId { get; set; }
+    }
+}