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/html.instructions.md

@@ -0,0 +1,11 @@
+---
+name: "HTML Standards"
+description: "Cross-project HTML standards for semantic structure and accessibility."
+applyTo: "**/*.html"
+---
+
+- Prefer semantic elements over generic wrappers.
+- Maintain accessible heading order and labels.
+- Keep layouts responsive and avoid inline styling where possible.
+- Avoid deprecated or non-semantic patterns.
+- Ensure keyboard and screen-reader-friendly markup for interactive elements.