chore: تنظیم Nexus برای NuGet و Docker offline

- Dockerfile: استفاده از Nexus Docker (194.5.195.53:32082)
- NuGet.config: استفاده از Nexus NuGet با HTTP و allowInsecureConnections
- workflow: حذف kubectl dependency، اضافه کردن 32082 به insecure-registries
- csproj: تغییر push آدرس به Nexus foursat-nuget-hosted

src/BackOffice.BFF.WebApi/NuGet.config

@@ -1,11 +1,18 @@
 <?xml version="1.0" encoding="utf-8"?>
 <configuration>
   <packageSources>
-    <add key="nuget.org" value="https://api.nuget.org/v3/index.json" protocolVersion="3" />
+    <clear />
+    <!-- Nexus as primary source (proxies nuget.org + caches packages) -->
+    <add key="Nexus" value="http://194.5.195.53:32081/repository/nuget-all/index.json" allowInsecureConnections="true" />
+    <!-- Backup: Direct Gitea registries -->
     <add key="FourSat" value="https://git.afrino.co/api/packages/FourSat/nuget/index.json" />
     <add key="Afrino" value="https://git.afrino.co/api/packages/Afrino/nuget/index.json" />
   </packageSources>
   <packageSourceCredentials>
+    <Nexus>
+      <add key="Username" value="admin" />
+      <add key="ClearTextPassword" value="87zH26nbqT" />
+    </Nexus>
     <FourSat>
       <add key="Username" value="masoud" />
       <add key="ClearTextPassword" value="87zH26nbqT" />