feat: Add implement skill documentation for PRD-based work

skills/engineering/implement/SKILL.md

@@ -0,0 +1,15 @@
+---
+name: implement
+description: "Implement a piece of work based on a PRD or set of issues."
+disable-model-invocation: true
+---
+
+Implement the work described by the user in the PRD or issues.
+
+Use /tdd where possible, at pre-agreed seams.
+
+Run typechecking regularly, single test files regularly, and the full test suite once at the end.
+
+Once done, use /review to review the work.
+
+Commit your work to the current branch.