CI/Docker: use SSL-free Nexus endpoints (mirror serves partial chain)

The HTTPS Nexus serves an incomplete cert chain that container trust stores
reject (NU1301 PartialChain / UNABLE_TO_GET_ISSUER), failing CI restore/install.
- NuGet has no strict-ssl flag → point CI + Dockerfile + compose at the plain-HTTP
  Nexus (http://171.22.25.73:8081, allowInsecureConnections) — no TLS, no cert check.
- npm: add --strict-ssl=false to the CI web-check install (Dockerfile already had it);
  Docker npm registry default also moved to the HTTP Nexus.
- ENV_FILE.example documents NUGET_INDEX/NPM_REGISTRY overrides.

Local dev (Windows trusts the cert) + image base pulls (Docker trusts it) are
unaffected — only in-container package feeds switch to HTTP.

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

server/Dockerfile

@@ -6,7 +6,7 @@ WORKDIR /src
 # NUGET_INDEX=http://<nexus-ip>:8081/repository/nuget-group/index.json for hosts
 # whose trust store lacks the mirror's intermediate (PartialChain) — e.g. local
 # Docker Desktop. allowInsecureConnections lets .NET 10 use the HTTP feed.
-ARG NUGET_INDEX=https://mirror.soroushasadi.com/repository/nuget-group/index.json
+ARG NUGET_INDEX=http://171.22.25.73:8081/repository/nuget-group/index.json
 RUN printf '%s\n' \
   '<?xml version="1.0" encoding="utf-8"?>' \
   '<configuration>' \