docs: add NetClaw tenant MCP setup guide

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Summary

• add a public, end-to-end NetClaw AI Assistant and tenant-scoped HTTP MCP guide
• rewrite the README around operator journeys and link the NetClaw guide prominently
• allow the now-public NetClaw name through the public-disclosure gate

Validation

• tools/ci/check-public-disclosure.sh
• Gitleaks v8.30.1 scan
• isolated NetClaw v0.26.0 CLI registration and secret/config separation check
• dotnet build Helpdesk.sln --configuration Release --no-restore
• dotnet test Helpdesk.sln --configuration Release --no-build --logger "console;verbosity=minimal"

Closes #65