Add new copilot instructions

[adegeo]

• I migrated the writing instructions to a new code file that should auto trigger on markdown content.
• I added some new instructions (you need to invoke manually via VSCode) for some common tasks I've run into.
• I added a prompt you can use in VSCode to update link text.

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Internal previews

📄 File	🔗 Preview link
.github/copilot-instructions.md	.NET Documentation Guidelines
.github/instructions/Markdown.WritingStyle.instructions.md	Markdown Writing Style Instructions
.github/instructions/Snippets.Migrate.instructions.md	.github/instructions/Snippets.Migrate.instructions
.github/instructions/Snippets.Push.instructions.md	Push inline code snippets to files
.github/prompts/Editing.FullPass.prompt.md	.github/prompts/Editing.FullPass.prompt
.github/prompts/RefreshLinks.prompt.md	Refresh Links Prompt

[Copilot]

Pull Request Overview

This PR migrates writing instructions to a new auto-triggering code file and adds Copilot instructions for common documentation tasks. The changes enhance the documentation workflow by providing structured guidance for snippet management, link updates, and writing style compliance.

Key Changes

• Migrated and streamlined writing style guidelines from general Copilot instructions to specialized auto-triggering instructions
• Added comprehensive snippet management instructions for pushing inline code to files and migrating legacy snippets
• Created a prompt for automated link text updates based on target content headings

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
.github/prompts/RefreshLinks.prompt.md	New prompt for automatically updating link text to match target content headings
.github/instructions/Snippets.Push.instructions.md	Instructions for extracting inline code blocks into standalone snippet files
.github/instructions/Snippets.Migrate.instructions.md	Guidelines for migrating legacy snippets from old to new repository structure
.github/instructions/Markdown.WritingStyle.instructions.md	Auto-triggering writing style guidelines for Markdown documentation
.github/copilot-instructions.md	Streamlined general Copilot instructions with updated AI usage disclosure guidelines

[wadepickett]

@adegeo, These copilot instruction files are excellent and a model to follow. Approved. I'm going to compare these with the collection we have for the ASP.NET Core docs repo to see if there is anything we might improve on based on yours.

I can't find any issues. It is well simplified, has concrete examples to follow, your formatting is effective for highlighting critical info for copilot (and humans.) Well done!