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/javascript.instructions.md

@@ -0,0 +1,15 @@
+---
+name: "JavaScript Standards"
+description: "Cross-project JavaScript and MJS standards for clarity, maintainability, and performance-aware code."
+applyTo: "**/*.js,**/*.mjs"
+---
+
+- Prefer `const` over `let`, and avoid `var`.
+- Use async/await for asynchronous flows.
+- Keep modules focused and avoid monolithic files.
+- Remove dead code and unused imports during related edits.
+- Use early returns to reduce branching complexity.
+- Keep behavior explicit; avoid implicit coercion and hidden side effects.
+- Favor composition and reusable utilities over duplicated logic.
+- Avoid deep nesting, callback-heavy control flow, and blocking sync work in user-facing paths.
+- Validate with the project's JavaScript lint, test, and build commands.