[TypeSpec Authoring] Consolidate reference documents to one place

[haolingdong-msft]

Summary

Consolidate the scattered reference documents used by the TypeSpec authoring skill into a single markdown file.

Background

Currently, reference documents are spread across multiple locations. This fragmentation makes it harder for both the skill and users to find the right information, and increases the maintenance burden when documents need to be updated.

Benefits

• This helps us update document links easily when some documents are 404.
• Later we can consider an automated process to sync the document references to this file.
• If users wants to add their own customized documents, like search team's case, they may be able to add their own document reference links in this file.

Parent Issue

Part of #14739