Rename llms/reference.txt to reference.md

The file is markdown-formatted and renders better on GitHub with .md extension.
The llms.txt standard name is preserved for the entry point file.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: richlander

llms.txt

@@ -1,7 +1,7 @@
 # .NET Release Metadata Graph
 > Machine-readable .NET release, CVE, and compatibility data for AI assistants.
 
-For extended reference with schema examples, see [llms/reference.txt](https://raw.githubusercontent.com/dotnet/core/refs/heads/release-index/llms/reference.txt).
+For extended reference with schema examples, see [llms/reference.md](https://raw.githubusercontent.com/dotnet/core/refs/heads/release-index/llms/reference.md).
 
 ## Rules
 

llms/reference.txt llms/reference.mdllms/reference.txt renamed to llms/reference.md

@@ -22,9 +22,9 @@
       "title": ".NET Release Timeline Index"
     },
     "llms-txt": {
-      "href": "https://raw.githubusercontent.com/dotnet/core/refs/heads/release-index/llms/reference.txt",
+      "href": "https://raw.githubusercontent.com/dotnet/core/refs/heads/release-index/llms/reference.md",
       "title": "LLM Quick Reference",
-      "type": "text/plain"
+      "type": "text/markdown"
     }
   },
   "_embedded": {