Added prompts to prepare GitHub PR and issue descriptions

[xperiandri]

Proposed Changes

Added a .github/PULL_REQUEST_TEMPLATE.md and two Copilot agent prompts under .github/prompts/:

• create-pr-description.prompt.md fills in the new PR template from the current branch's diff and commit history.
• create-issue-description.prompt.md fills in the existing .github/ISSUE_TEMPLATE.md the same way.

Both prompts compare the current branch against origin/dev, the default branch of this repository.

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• Build and tests pass locally — no code changes; nothing to build or test
• I have added tests that prove my fix is effective or that my feature works (if appropriate) — not applicable, these are Copilot prompt/template files
• I have added necessary documentation (if appropriate) — the prompts and template are self-documenting

🤖 Generated with Claude Code

[valbers]

Why this:

• Use only en dashes (–) for dashes; never use em dashes (—).

?