[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/Pages/Admin/Settings.cshtml

@@ -73,6 +73,11 @@
                         <input type="checkbox" name="AiAutoApprove" value="true" checked="@Model.AiAutoApprove" />
                         <span class="t-body"><span>در حالت خودکار، آگهی‌هایی که AI تأیید می‌کند مستقیم منتشر شوند</span></span>
                     </label>
+                    <label class="toggle-row">
+                        <input type="checkbox" name="AiUseProxy" value="true" checked="@Model.AiUseProxy" />
+                        <span class="t-body"><span>ارسال درخواست هوش مصنوعی از طریق پروکسی</span>
+                            <span class="t-hint">برای دسترسی به سرویس‌هایی مثل OpenAI از داخل ایران؛ از همان آدرس پروکسی تب «منابع جمع‌آوری» استفاده می‌کند.</span></span>
+                    </label>
                 </section>
 
                 <!-- SOURCES -->

src/JobsMedical.Web/Pages/Admin/Settings.cshtml.cs

@@ -29,6 +29,7 @@ public class SettingsModel : PageModel
     [BindProperty] public string? AiModel { get; set; }
     [BindProperty] public string AiSystemPrompt { get; set; } = "";
     [BindProperty] public bool AiAutoApprove { get; set; }
+    [BindProperty] public bool AiUseProxy { get; set; }
     // Channel scraping sources
     [BindProperty] public bool AutoIngestEnabled { get; set; }
     [BindProperty] public int IngestIntervalMinutes { get; set; } = 30;
@@ -76,6 +77,7 @@ public class SettingsModel : PageModel
         AiModel = s.AiModel;
         AiSystemPrompt = s.AiSystemPrompt;
         AiAutoApprove = s.AiAutoApprove;
+        AiUseProxy = s.AiUseProxy;
         AutoIngestEnabled = s.AutoIngestEnabled;
         IngestIntervalMinutes = s.IngestIntervalMinutes;
         TelegramEnabled = s.TelegramEnabled;
@@ -120,6 +122,7 @@ public class SettingsModel : PageModel
             AiModel = AiModel,
             AiSystemPrompt = AiSystemPrompt,
             AiAutoApprove = AiAutoApprove,
+            AiUseProxy = AiUseProxy,
             AutoIngestEnabled = AutoIngestEnabled,
             IngestIntervalMinutes = IngestIntervalMinutes,
             TelegramEnabled = TelegramEnabled,