W-23612601 Rename LLM Proxy to Model Proxy

[glenn-rodgers-sf]

Summary

Rename "LLM Proxy" to "Model Proxy" across Agent Network documentation.

Content replacements (case-preserving)

• LLM Proxy/LLM Proxies → Model Proxy/Model Proxies in:
  • agent-network/1.0/modules/ROOT/pages/af-agent-networks.adoc
  • agent-network/1.0/modules/ROOT/pages/af-project-files.adoc
  • agent-network/2.0/modules/ROOT/pages/af-agent-networks.adoc
• Fixed article grammar (an Model Proxy → a Model Proxy).

Reference updates

• Cross-repo xrefs updated for the page move from the gateway to the general component:
  • xref:gateway::flex-gateway-llm-proxy.adoc → xref:general::model-proxy.adoc (anchors preserved, e.g. #supported-llm-providers).

Not changed

• No x-llm-proxy-* HTTP headers present in these files.
• No file renames required (no llm-proxy filenames in this repo).