chore(prompts): add skill and prompt to update supported Go versions

[ccojocar]

Summary

• add a reusable skill to update supported Go versions based on https://go.dev/doc/devel/release
• add a /prompts-callable prompt that invokes the skill
• include a careful repository-wide discovery checklist for all active Go-version usages
• include validation, branch/commit/push, and PR-creation workflow in the skill contract

Reference

• Example update PR pattern: Add support for go 1.26.x and remove support for go 1.24.x #1508

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.61%. Comparing base (84df6fa) to head (2048d75).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1561   +/-   ##
=======================================
  Coverage   80.61%   80.61%           
=======================================
  Files         104      104           
  Lines        9851     9851           
=======================================
  Hits         7941     7941           
  Misses       1421     1421           
  Partials      489      489           

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