Add shared instruction files and copilot history maintenance scripts

- Add 12 cross-project instruction files to resources/instructions/
- Add cleanup-copilot-history.mjs/.sh: quarantine-based history cleanup with dry-run and aggressive scope
- Add restore-copilot-history.mjs/.sh: restore from quarantine by run, path, or filter
- Add purge-copilot-history-quarantine.mjs/.sh: purge old quarantine runs with keep-latest guard
- Add copilot-history-maintenance.test.mjs: 3 passing unit tests covering all three scripts

resources/instructions/yaml.instructions.md

@@ -0,0 +1,11 @@
+---
+name: "YAML Standards"
+description: "Cross-project YAML standards for readable and consistent configuration files."
+applyTo: "**/*.yml,**/*.yaml"
+---
+
+- Use consistent indentation and spacing.
+- Keep values explicit and structures readable.
+- Avoid overly complex inline expressions.
+- Keep file conventions consistent within each configuration domain.
+- Keep YAML yamllint-compatible where feasible.