[westey (westey-m)]

Why are these changes needed?

Replace the README maintenance-mode warning with explicit language stating that AutoGen is archived and no longer maintained by Microsoft. Clarify that Microsoft is not providing bug fixes, security fixes, new features, or support, and that the repository remains available for historical/reference purposes.

Align the status badge and the remaining maintenance-mode reference with the warning while preserving the Microsoft Agent Framework migration links.

Related issue number

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://github.com/microsoft/autogen/blob/main/CONTRIBUTING.md to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.23%. Comparing base (027ecf0) to head (dcf0d74).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #8366   +/-   ##
=======================================
  Coverage   81.23%   81.23%           
=======================================
  Files         244      244           
  Lines       18527    18527           
=======================================
  Hits        15050    15050           
  Misses       3477     3477           

Flag	Coverage Δ
unittests	81.23% <ø> (ø)

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