[Ingest] Per-source proxy toggle instead of one global switch

Each ingestion source now decides independently whether to route through the proxy: added TelegramUseProxy/BaleUseProxy/DivarUseProxy/MedjobsUseProxy/WebsitesUseProxy flags (migration). ScrapeHttpClients.For(s, useProxy) takes the source's own flag; a source is proxied only when its flag is on AND a proxy URL is set. Settings 'sources' tab: removed the global enable checkbox, kept the proxy address field, and added an «از پروکسی استفاده شود» checkbox under each source. Old IngestProxyEnabled column kept for compatibility but no longer gates routing.

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

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

@@ -19,10 +19,11 @@ public sealed class ScrapeHttpClients : IDisposable
 {
     private readonly ConcurrentDictionary<string, HttpClient> _cache = new();
 
-    /// <summary>The HttpClient for the given settings — proxied when enabled, direct otherwise.</summary>
-    public HttpClient For(AppSetting s)
+    /// <summary>The HttpClient for a source — proxied only when that source opts in AND a proxy
+    /// URL is configured; otherwise a direct client. Pass the source's own per-source flag.</summary>
+    public HttpClient For(AppSetting s, bool useProxy)
     {
-        var key = (s.IngestProxyEnabled && !string.IsNullOrWhiteSpace(s.IngestProxyUrl))
+        var key = (useProxy && !string.IsNullOrWhiteSpace(s.IngestProxyUrl))
             ? s.IngestProxyUrl.Trim()
             : "direct";