feat: update README.md paths and clean up Directory.Build.props

[wangkanai]

This pull request refactors how NuGet package metadata and assets (such as icons and README files) are included for the Federation, Identity, and Security projects. The main goal is to centralize and standardize the way these files are referenced and packaged, improving maintainability and consistency across the projects.

Centralization and Standardization of Package Metadata and Assets:

• Moved the <PackageIcon> and <PackageReadmeFile> properties from individual project-level Directory.Build.props files to the root Directory.Build.props, ensuring consistent package metadata for all projects under src. [1] [2] [3] [4]
• Updated asset inclusion (README.md and logo files) in all affected projects to use the $(RepoRoot) property, ensuring correct file paths and reducing duplication or errors from relative paths. [1] [2] [3] [4]
• Removed redundant or now-unnecessary property and item group definitions from the individual project Directory.Build.props files, as these are now handled centrally. [1] [2] [3]

These changes streamline the packaging process and make it easier to maintain consistent NuGet package metadata and assets across multiple projects.

[Copilot]

Pull Request Overview

This pull request centralizes NuGet package metadata and asset references by moving common properties to the root Directory.Build.props file and updating file paths to use the $(RepoRoot) property for consistency.

• Moved PackageIcon and PackageReadmeFile properties from individual project Directory.Build.props files to the root level
• Updated README.md file references to use absolute paths with $(RepoRoot) instead of relative paths
• Removed redundant package metadata properties from Federation, Identity, and Security project configurations

Reviewed Changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 3 comments.

File	Description
Directory.Build.props	Added centralized package metadata properties for src projects
Federation/Directory.Build.props	Removed redundant package properties and updated README path
Identity/Directory.Build.props	Removed redundant package properties and updated README path
Security/Directory.Build.props	Removed redundant package properties and updated README path

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