fix(gateway): restore safe search fallback

Fall back to guarded Chat Completions answers when DeepSeek web search fails so grounded current-information hints do not surface generic provider errors.

src/main/kotlin/com/osglab/account/features/gateway/providers/deepseek/DeepSeekResponsesClient.kt

@@ -9,6 +9,7 @@ import com.osglab.account.features.gateway.models.ProviderOutput
 import com.osglab.account.features.gateway.models.ProviderUsage
 import com.osglab.account.features.gateway.models.TextProviderRequest
 import com.osglab.account.features.gateway.models.UsageMeter
+import com.osglab.account.features.gateway.providers.ProviderUpstreamException
 import io.ktor.client.HttpClient
 import io.ktor.client.call.body
 import io.ktor.client.request.bearerAuth
@@ -72,16 +73,16 @@ internal class DeepSeekSearchFallbackClient(
         } catch (failure: CancellationException) {
             throw failure
         } catch (failure: Exception) {
+            val upstreamStatus = (failure as? ProviderUpstreamException)?.upstreamStatus
             LOG.warn(
-                "DeepSeek search path failed requestId={} taskKind={} searchMode={} failureType={}",
+                "DeepSeek search path failed requestId={} taskKind={} searchMode={} " +
+                    "failureType={} upstreamStatus={} fallback=chat_completions",
                 request.requestId,
                 request.executionPolicy.taskKind.name,
                 request.executionPolicy.webSearch.name,
                 failure::class.simpleName ?: "Exception",
+                upstreamStatus ?: "unknown",
             )
-            if (request.executionPolicy.webSearch == GatewayWebSearchMode.REQUIRED) {
-                throw failure
-            }
             return fallback.complete(
                 request.copy(
                     executionPolicy = request.executionPolicy.copy(