feat(ai): DB-only config + runtime provider selection via factory

API/ROLAC.API/Services/Ai/GeminiExpenseAiService.cs

@@ -1,6 +1,5 @@
 using System.Net.Http.Json;
 using System.Text.Json;
-using Microsoft.Extensions.Options;
 using ROLAC.API.Data;
 
 namespace ROLAC.API.Services.Ai;
@@ -12,25 +11,28 @@ namespace ROLAC.API.Services.Ai;
 /// </summary>
 public sealed class GeminiExpenseAiService : ExpenseAiServiceBase
 {
+    private const string BaseUrl = "https://generativelanguage.googleapis.com/v1beta";
+
     private readonly HttpClient _http;
-    private readonly GeminiOptions _options;
+    private readonly IChurchAiConfigProvider _config;
     private readonly ILogger<GeminiExpenseAiService> _logger;
 
     public GeminiExpenseAiService(
         HttpClient http,
-        IOptions<GeminiOptions> options,
+        IChurchAiConfigProvider config,
         AppDbContext db,
         ILogger<GeminiExpenseAiService> logger)
         : base(db)
     {
         _http = http;
-        _options = options.Value;
+        _config = config;
         _logger = logger;
     }
 
     protected override async Task<ModelAnswer?> CallModelAsync(string prompt, CancellationToken ct)
     {
-        if (string.IsNullOrWhiteSpace(_options.ApiKey))
+        var cfg = await _config.GetAsync(ct);
+        if (string.IsNullOrWhiteSpace(cfg.GeminiApiKey))
         {
             _logger.LogWarning("Gemini API key is not configured; expense AI assist is disabled.");
             return null;
@@ -63,12 +65,12 @@ public sealed class GeminiExpenseAiService : ExpenseAiServiceBase
                 },
             };
 
-            var url = $"{_options.BaseUrl}/models/{_options.Model}:generateContent";
+            var url = $"{BaseUrl}/models/{cfg.GeminiModel}:generateContent";
             using var request = new HttpRequestMessage(HttpMethod.Post, url)
             {
                 Content = JsonContent.Create(payload),
             };
-            request.Headers.Add("X-goog-api-key", _options.ApiKey);
+            request.Headers.Add("X-goog-api-key", cfg.GeminiApiKey);
 
             using var response = await _http.SendAsync(request, ct);
             if (!response.IsSuccessStatusCode)