Refresh root README for repo move and multi-language positioning

[davidfowl]

Description

Refresh the root README after the move to microsoft/aspire and tighten the top-level messaging so it reads less like a .NET-only project.

This updates the opening description, adds a small C# and TypeScript app definition example, refreshes the useful links section, and removes stale repo/org and .NET Foundation references from the root README.

No additional dependencies are required for this change.

Validation:

• git diff --check -- README.md

Fixes # (issue)

Checklist

• Is this feature complete?
  • Yes. Ready to ship.
  • No. Follow-up changes expected.
• Are you including unit tests for the changes and scenario tests if relevant?
  • Yes
  • No
• Did you add public API?
  • Yes
    • If yes, did you have an API Review for it?
      • Yes
      • No
    • Did you add <remarks /> and <code /> elements on your triple slash comments?
      • Yes
      • No
  • No
• Does the change make any security assumptions or guarantees?
  • Yes
    • If yes, have you done a threat model and had a security review?
      • Yes
      • No
  • No
• Does the change require an update in our Aspire docs?
  • Yes
    • Link to aspire.dev issue:
      • New issue
  • No

[github-actions]

🚀 Dogfood this PR with:

⚠️ WARNING: Do not do this without first carefully reviewing the code of this PR to satisfy yourself it is safe.

curl -fsSL https://raw.githubusercontent.com/microsoft/aspire/main/eng/scripts/get-aspire-cli-pr.sh | bash -s -- 15480

Or

• Run remotely in PowerShell:

iex "& { $(irm https://raw.githubusercontent.com/microsoft/aspire/main/eng/scripts/get-aspire-cli-pr.ps1) } 15480"

[Copilot]

Pull request overview

Updates the repository’s root README to reflect the move to microsoft/aspire and reposition Aspire as a multi-language toolchain (not just .NET-centric), with refreshed examples and links.

Changes:

• Reworks the “What is Aspire?” intro copy and adds a CI workflow badge.
• Adds a “simple app definition” section with C# and TypeScript AppHost examples.
• Refreshes the “Useful links” section and removes stale/legacy references.

[maddymontaquila]

This looks good. we should work on aligning closer to the homepage at some point (for SEO references) but for tomorrow i think this is perfect.

[joperezr]

@microsoft-github-policy-service rerun