[AI] Route AI calls through the Xray/V2Ray proxy (reach OpenAI from Iran)

Add AiUseProxy setting + a toggle in the AI settings section. ScrapeHttpClients.ForAi(settings) returns a proxied HttpClient (reusing IngestProxyUrl, 100s timeout) when AiUseProxy is on, otherwise direct; AI-cache keys are protected from the scrape-client cleanup. OpenAiCompatibleAuditor now uses it, so the AI auditor (e.g. api.openai.com) is reachable through the same Xray sidecar that serves Telegram. Migration adds the column.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/JobsMedical.Web/Services/Scraping/AiAuditor.cs

@@ -30,12 +30,12 @@ public interface IAiAuditor
 /// </summary>
 public class OpenAiCompatibleAuditor : IAiAuditor
 {
-    private readonly IHttpClientFactory _http;
+    private readonly ScrapeHttpClients _clients;
     private readonly ILogger<OpenAiCompatibleAuditor> _log;
 
-    public OpenAiCompatibleAuditor(IHttpClientFactory http, ILogger<OpenAiCompatibleAuditor> log)
+    public OpenAiCompatibleAuditor(ScrapeHttpClients clients, ILogger<OpenAiCompatibleAuditor> log)
     {
-        _http = http;
+        _clients = clients;
         _log = log;
     }
 
@@ -57,8 +57,7 @@ public class OpenAiCompatibleAuditor : IAiAuditor
                 },
             };
 
-            var client = _http.CreateClient("ai");
-            client.Timeout = TimeSpan.FromSeconds(30);
+            var client = _clients.ForAi(s);   // proxy-aware when AiUseProxy is on (e.g. OpenAI from Iran)
             using var req = new HttpRequestMessage(HttpMethod.Post, s.AiEndpoint)
             {
                 Content = new StringContent(JsonSerializer.Serialize(payload), Encoding.UTF8, "application/json"),