NuGet: drop Liara from root nuget.config too (Nexus-only everywhere)

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

.gitea/workflows/ci-cd.yml

@@ -39,9 +39,10 @@ jobs:
           git fetch --depth=1 origin "${REF}"
           git checkout FETCH_HEAD
 
-      - name: Write NuGet config (Nexus group primary; Liara fallback)
-        # Nexus nuget-group is the primary mirror; Liara is kept as a fallback so a
-        # single mirror outage (e.g. a 500 on the service index) doesn't break restore.
+      - name: Write NuGet config (Nexus only)
+        # Single source = our Nexus mirror. We do NOT list Liara as a fallback: NuGet loads
+        # the service index of EVERY configured source, so a 500 from a fallback aborts the
+        # whole restore (NU1301). Nexus is the source of truth.
         run: |
           cat > /tmp/nuget.ci.config << 'EOF'
           <?xml version="1.0" encoding="utf-8"?>
@@ -51,9 +52,6 @@ jobs:
               <add key="nexus"
                    value="https://mirror.soroushasadi.com/repository/nuget-group/index.json"
                    protocolVersion="3" />
-              <add key="liara"
-                   value="https://package-mirror.liara.ir/repository/nuget/index.json"
-                   protocolVersion="3" />
             </packageSources>
             <config>
               <add key="http_retry_count" value="6" />

nuget.config

@@ -2,9 +2,9 @@
 <configuration>
   <packageSources>
     <clear />
-    <!-- Soroush Nexus mirror (primary) + Liara mirror (fallback) — nuget.org is filtered. -->
+    <!-- Single source: Soroush Nexus mirror. No Liara fallback — NuGet probes every
+         listed source's index, so a dead fallback (500) aborts the whole restore. -->
     <add key="nexus" value="https://mirror.soroushasadi.com/repository/nuget-group/index.json" protocolVersion="3" />
-    <add key="liara" value="https://package-mirror.liara.ir/repository/nuget/index.json" protocolVersion="3" />
   </packageSources>
   <config>
     <add key="http_retry_count" value="6" />

nuget.docker.config

@@ -1,9 +1,10 @@
 <?xml version="1.0" encoding="utf-8"?>
 <!--
-  NuGet sources for the Docker image build (Linux .NET — runs `dotnet restore`
-  inside the SDK container). Nexus nuget-group is primary; Liara is kept as a
-  fallback so a single mirror outage doesn't break the build. nuget.org is
-  filtered in Iran, so it is intentionally not listed.
+  NuGet source for the Docker image build (Linux .NET — runs `dotnet restore`
+  inside the SDK container). Single source = our Nexus mirror. We deliberately
+  do NOT list a fallback: NuGet loads the service index of every configured
+  source, so a 500 from a fallback would abort the whole restore. nuget.org is
+  filtered in Iran and is intentionally absent — Nexus is the source of truth.
 -->
 <configuration>
   <packageSources>
@@ -11,9 +12,6 @@
     <add key="nexus"
          value="https://mirror.soroushasadi.com/repository/nuget-group/index.json"
          protocolVersion="3" />
-    <add key="liara"
-         value="https://package-mirror.liara.ir/repository/nuget/index.json"
-         protocolVersion="3" />
   </packageSources>
   <config>
     <add key="http_retry_count" value="8" />