Add What's new in .NET 11 Preview 1 documentation

[Copilot]

Plan: Create What's new in .NET 11 articles for Preview 1

• Create directory structure for .NET 11 what's new articles
• Create overview.md for .NET 11
• Create runtime.md for .NET 11
• Create libraries.md for .NET 11
• Create sdk.md for .NET 11
• Update fundamentals TOC to include .NET 11 what's new articles
• Update fundamentals TOC to include existing .NET 11 breaking changes
• Verify all articles follow documentation standards
• Test build and validate links
• Address review feedback:
  • Updated intro paragraph in all 4 articles to "It was last updated for Preview 1"
  • Removed blank titleSuffix from all articles (first round)
  • Removed blank lines from breaking changes list in libraries.md
  • Added C# 15 section to overview.md
  • Updated docs/whats-new/index.yml to include .NET 11 section
• Address additional review feedback:
  • Added titleSuffix: "" and ms.update-cycle: 3650-days to all 4 articles
  • Updated ms.date in index.yml from 07/01/2025 to 02/10/2026
  • Fixed ASP.NET Core link in index.yml to use /aspnet/core/release-notes/aspnetcore-11.0 (consistent with .NET 10 pattern)

Original prompt

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This section details on the original issue you should resolve

<issue_title>[New article]: What's new in .NET 11</issue_title>
<issue_description>Use the prompt in https://github.com/dotnet/docs/blob/main/.github/prompts/whats-new-net.md to create the "What's new" articles for .NET 11, as of Preview 1.

You'll need to create new articles, and add new nodes to the fundamentals TOC for .NET 11. When you edit the TOC, include the existing article for breaking changes in .NET 11 (as of preview 1).</issue_description>

<agent_instructions>You can see the example TOC changes in this closed PR: #51577</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes [New article]: What's new in .NET 11 #51579

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Internal previews

📄 File	🔗 Preview link
docs/core/whats-new/dotnet-11/libraries.md	docs/core/whats-new/dotnet-11/libraries
docs/core/whats-new/dotnet-11/overview.md	docs/core/whats-new/dotnet-11/overview
docs/core/whats-new/dotnet-11/runtime.md	docs/core/whats-new/dotnet-11/runtime
docs/core/whats-new/dotnet-11/sdk.md	docs/core/whats-new/dotnet-11/sdk
docs/fundamentals/toc.yml	docs/fundamentals/toc
docs/whats-new/index.yml	docs/whats-new/index

[BillWagner]

@copilot I have comments for you to address

In addition to the comments on specifics in this PR, update https://github.com/dotnet/docs/blob/main/docs/whats-new/index.yml to include a block for .NET 11 with links to this article

[BillWagner]

@copilot Please address all review comments

[Copilot]

@copilot I have comments for you to address

In addition to the comments on specifics in this PR, update https://github.com/dotnet/docs/blob/main/docs/whats-new/index.yml to include a block for .NET...

All review comments addressed and docs/whats-new/index.yml updated with .NET 11 section. Commit a69e163

[BillWagner]

One more update, and then this is ready.

[Copilot]

Pull request overview

Adds the initial “What’s new in .NET 11 (Preview 1)” documentation set and wires it into the docs navigation so readers can find the new content from the fundamentals TOC and the global “What’s new” landing page.

Changes:

• Added new .NET 11 “What’s new” articles: overview, runtime, libraries, and SDK.
• Updated docs/fundamentals/toc.yml to include the new .NET 11 articles alongside existing .NET 11 breaking changes.
• Updated docs/whats-new/index.yml to add a .NET 11 section on the landing page.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 10 comments.

Show a summary per file

File	Description
docs/whats-new/index.yml	Adds a .NET 11 entry to the “What’s new” landing page.
docs/fundamentals/toc.yml	Adds TOC nodes for the .NET 11 “What’s new” articles and links breaking changes.
docs/core/whats-new/dotnet-11/sdk.md	New .NET 11 SDK/tooling “what’s new” article with a breaking change highlight.
docs/core/whats-new/dotnet-11/runtime.md	New .NET 11 runtime “what’s new” article focusing on hardware baseline changes.
docs/core/whats-new/dotnet-11/overview.md	New .NET 11 overview page linking to the runtime, libraries, SDK, and other areas.
docs/core/whats-new/dotnet-11/libraries.md	New .NET 11 libraries “what’s new” article summarizing API and behavior changes.