feat: add create-update-pr skill

[hwbrzzl]

Summary

• Adds a create-update-pr Copilot skill that automates PR creation and description formatting
• Enforces a strict two-section PR body format with separate rules for feature and bug-fix PRs
• Implements a nine-step workflow covering branch detection, diff analysis, body composition, and PR creation or update

Why

Pull request descriptions in this repository previously lacked a consistent structure, making reviews harder and change history less traceable. This skill gives the AI agent a repeatable spec-driven procedure for writing PR bodies so every PR follows the same format without manual effort.

When triggered, the skill detects the current branch and any linked issue number, computes the diff against origin/master, derives behavior-oriented summary bullets, and creates or updates the PR via gh pr create or gh pr edit. The resulting body always contains a Summary section with 2-3 behavior bullets and a Why section with explanatory prose and real user-facing code examples derived from test cases.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 67.98%. Comparing base (966a11f) to head (1a80ace).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1419   +/-   ##
=======================================
  Coverage   67.97%   67.98%           
=======================================
  Files         354      354           
  Lines       27521    27521           
=======================================
+ Hits        18708    18710    +2     
+ Misses       7964     7963    -1     
+ Partials      849      848    -1     

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