docs: celebrate releases with a README smile

[zimeg]

Summary

• Add 🙂 to the README's latest release heading, matching its existing emoji style.
• Keep this PR scoped to the README; Maintainers' Guide updates remain planned only.

Validation

• Passed: git diff --check
• Application tests not run (documentation-only change).

[zimeg]

🎣 Ignore me I am testing "things"

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.21%. Comparing base (a9bda96) to head (26ffc8e).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #692   +/-   ##
=======================================
  Coverage   78.21%   78.21%           
=======================================
  Files         239      239           
  Lines       18127    18127           
=======================================
  Hits        14178    14178           
  Misses       3949     3949           

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