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/env-config.instructions.md

@@ -0,0 +1,12 @@
+---
+name: "Environment and Config Standards"
+description: "Cross-project standards for env and conf files, with secure configuration defaults."
+applyTo: "**/*.env,**/*.env.*,**/*.conf"
+---
+
+- Keep secrets out of source-controlled env files.
+- Use environment-specific overrides instead of duplicating large config blocks.
+- Keep `.example` templates free of real credentials.
+- Document required variables and reasonable defaults.
+- Prefer least-privilege and secret isolation practices.
+- Ensure runtime/deploy scripts fail clearly when required variables are missing.