Add PR creation skill for Copilot

Add .github/instructions/pr.instructions.md to ensure PRs always include a bug or debt label.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: bschnurr

.github/instructions/pr.instructions.md

@@ -0,0 +1,10 @@
+---
+description: When creating pull requests
+---
+
+# PR Creation Skill
+
+When creating pull requests, always include one of these labels:
+
+- `bug` — for bug fixes
+- `debt` — for technical debt improvements