docs: add agent guidance files and templates

.claude/skills/implement-plan/SKILL.md

@@ -0,0 +1,30 @@
+---
+description: Implement an approved plan with minimal scope, tests, and verification. Use after the user approves a plan.
+disable-model-invocation: true
+---
+
+Implement the approved plan.
+
+Rules:
+
+- Follow the approved plan exactly.
+- Keep the diff minimal.
+- Do not refactor unrelated code.
+- Do not change behavior outside the task scope.
+- Add or update tests for changed behavior.
+- Run the verification commands from the plan or task brief.
+- Fix failures caused by your changes.
+- Stop and explain before expanding scope.
+- If a verification command is unavailable, explain why.
+
+Final report:
+
+## Summary
+
+## Files changed
+
+## Tests added or updated
+
+## Commands run
+
+## Remaining risks