Add CA2266 analyzer documentation

[Copilot]

Related to dotnet/sdk#53749 (comment).

---

CA2266 was introduced for file-based apps, but the docs set did not include a rule page or links from the analyzer indexes. This change adds the missing rule documentation and wires it into the relevant .NET 10 and code analysis entry points.

• New rule article

  • Adds CA2266: File-based program entry point should start with '#!'
  • Documents the rule cause, guidance, suppression details, and related file-based app docs

• Analyzer index updates

  • Adds CA2266 to the usage warnings index
  • Adds CA2266 to the main quality rules index
  • Adds CA2266 to the code analysis overview table for .NET 10

• Navigation and discovery

  • Adds CA2266 to the tools diagnostics TOC
  • Links the rule from the .NET 10 SDK “file-based apps” content so the analyzer is discoverable from the feature docs

• Example

  // app.cs
  #:include "helpers.cs"
  
  Console.WriteLine(GetMessage());

  // app.cs
  #!/usr/bin/env dotnet
  #:include "helpers.cs"
  
  Console.WriteLine(GetMessage());

---

Internal previews

📄 File	🔗 Preview link
docs/fundamentals/code-analysis/overview.md	docs/fundamentals/code-analysis/overview
docs/fundamentals/code-analysis/quality-rules/ca2266.md	docs/fundamentals/code-analysis/quality-rules/ca2266
docs/fundamentals/code-analysis/quality-rules/index.md	docs/fundamentals/code-analysis/quality-rules/index
docs/fundamentals/code-analysis/quality-rules/usage-warnings.md	docs/fundamentals/code-analysis/quality-rules/usage-warnings
docs/navigate/tools-diagnostics/toc.yml	docs/navigate/tools-diagnostics/toc

[Copilot]

Pull request overview

Adds documentation for the new CA2266 analyzer rule (file-based apps shebang requirement) and connects the new rule page to the existing code analysis indexes, TOC navigation, and .NET 10 SDK “file-based apps” content so users can discover it.

Changes:

• Adds a new rule article for CA2266 under code quality rules.
• Updates rule indexes and the .NET 10 “enabled rules” table to include CA2266.
• Adds CA2266 to the tools diagnostics TOC and links to it from the .NET 10 SDK file-based apps section.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
docs/navigate/tools-diagnostics/toc.yml	Adds CA2266 to the Code quality → Usage rules navigation.
docs/fundamentals/code-analysis/quality-rules/usage-warnings.md	Adds CA2266 to the Usage rules index table.
docs/fundamentals/code-analysis/quality-rules/index.md	Adds CA2266 to the main quality rules index table.
docs/fundamentals/code-analysis/quality-rules/ca2266.md	New CA2266 rule documentation page (cause, guidance, suppression, and example).
docs/fundamentals/code-analysis/overview.md	Adds CA2266 to the .NET 10 enabled-by-default rules table.
docs/core/whats-new/dotnet-10/sdk.md	Links CA2266 from the .NET 10 file-based apps enhancements section.

[jjonescz]

@copilot

[BillWagner]

This LGTM, but I'll let @gewarren check as well.