Escalate provider fetch failures to Error for alert emails

HTTP and Playwright fetch failures in HtmlJobSearcher are now logged at
Error so that Serilog's email sink triggers an alert when a job provider
is unreachable. Per-URL match failures remain at Warning (expected noise).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Jobs/cv-search-job/Services/HtmlJobSearcher.cs

@@ -125,7 +125,7 @@ public sealed class HtmlJobSearcher
         }
         catch (Exception ex)
         {
-            _logger.LogWarning(ex, "Provider {Provider}: HTTP fetch failed for {Url}", providerName, url);
+            _logger.LogError(ex, "Provider {Provider}: HTTP fetch failed for {Url}", providerName, url);
             return null;
         }
     }
@@ -169,7 +169,7 @@ public sealed class HtmlJobSearcher
         }
         catch (Exception ex)
         {
-            _logger.LogWarning(ex, "Provider {Provider}: Playwright fetch failed for {Url}", providerName, url);
+            _logger.LogError(ex, "Provider {Provider}: Playwright fetch failed for {Url}", providerName, url);
             return null;
         }
     }