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/engineering-best-practices.instructions.md

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+---
+name: "Global Engineering Best Practices"
+description: "Umbrella baseline for cross-project engineering guidance."
+applyTo: "**"
+---
+
+- Use `engineering-core-defaults.instructions.md` for global engineering behavior.
+- Use `language-and-tooling-defaults.instructions.md` for file-type and tooling baselines.
+- When project-local instructions are present, treat them as the authoritative source.

resources/instructions/engineering-core-defaults.instructions.md

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+---
+name: "Engineering Core Defaults"
+description: "Cross-project baseline for maintainable, predictable, and secure engineering decisions."
+applyTo: "**"
+---
+
+- Prioritize maintainability, readability, and predictability over novelty.
+- Prefer explicit behavior and descriptive names over implicit shortcuts.
+- Reuse existing project patterns and utilities before introducing abstractions.
+- Keep implementations modular and scoped; avoid monolithic files and deep nesting.
+- Remove dead code, unused imports, and duplicate logic when touching related areas.
+- Add comments only for non-obvious intent, trade-offs, or constraints.
+- Favor composition over inheritance and use early returns to simplify control flow.
+- Default to secure practices: validate inputs, isolate secrets, and avoid hardcoded credentials.
+- Keep dependencies minimal and add new ones only with clear justification.
+- Optimize for practical performance without reducing clarity or maintainability.
+- Treat project-local instructions as authoritative when they conflict with global defaults.

resources/instructions/env-config.instructions.md

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+---
+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.

resources/instructions/html.instructions.md

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+---
+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.

resources/instructions/javascript.instructions.md

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+---
+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.

resources/instructions/json.instructions.md

@@ -0,0 +1,12 @@
+---
+name: "JSON Standards"
+description: "Cross-project JSON standards for stable structure and deterministic formatting."
+applyTo: "**/*.json"
+---
+
+- Keep JSON formatting consistent and deterministic.
+- Avoid duplicate keys and ambiguous nesting.
+- Prefer stable, explicit property names.
+- Remove unused configuration fields during related edits.
+- Preserve existing data contracts unless intentional changes are documented.
+- Validate JSON syntax before commit.

resources/instructions/language-and-tooling-defaults.instructions.md

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+---
+name: "Language and Tooling Defaults"
+description: "Cross-project language and file-type guidance for JS, Vue, SCSS, Markdown, JSON, HTML, Shell, YAML, and config files."
+applyTo: "**/*.js,**/*.mjs,**/*.vue,**/*.scss,**/*.md,**/*.json,**/*.html,**/*.sh,**/*.yml,**/*.yaml,**/*.env,**/*.conf"
+---
+
+- Use `javascript.instructions.md` for JavaScript and MJS files.
+- Use `vue.instructions.md` for Vue SFC files.
+- Use `scss.instructions.md` for SCSS stylesheets.
+- Use `markdown.instructions.md` for Markdown docs.
+- Use `json.instructions.md` for JSON data/config files.
+- Use `html.instructions.md` for HTML templates/pages.
+- Use `shell.instructions.md` for shell scripts.
+- Use `yaml.instructions.md` for YAML configs.
+- Use `env-config.instructions.md` for env and conf files.
+- Prefer project-local instructions when they provide more specific guidance.

resources/instructions/markdown.instructions.md

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+---
+name: "Markdown Standards"
+description: "Cross-project Markdown standards for concise, scan-friendly documentation."
+applyTo: "**/*.md"
+---
+
+- Keep documents concise, structured, and easy to scan.
+- Use consistent heading hierarchy.
+- Prefer bullet lists and tables for structured content.
+- Avoid large unbroken paragraphs.
+- Use examples where they improve clarity.
+- Keep formatting markdownlint-compatible when possible.

resources/instructions/scss.instructions.md

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+---
+name: "SCSS Standards"
+description: "Cross-project SCSS standards for modular styling and maintainable selector design."
+applyTo: "**/*.scss"
+---
+
+- Keep selectors shallow and specificity low.
+- Reuse variables and mixins instead of repeating style constants.
+- Keep style modules focused; avoid monolithic stylesheet files.
+- Avoid deep nesting and `!important` except as a last resort.
+- Remove duplicated selectors and dead style rules during related edits.
+- Prefer design-token reuse before adding new primitives.
+- Validate with project style lint/build commands when available.

resources/instructions/shell.instructions.md

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+---
+name: "Shell Standards"
+description: "Cross-project shell scripting standards for safety and predictable automation."
+applyTo: "**/*.sh"
+---
+
+- Use defensive scripting with explicit error handling.
+- Quote variables and paths.
+- Validate inputs before using them in commands.
+- Keep scripts modular and avoid hidden side effects.
+- Avoid unsafe deletion patterns, silent failures, and hardcoded environment-specific paths.
+- Keep scripts ShellCheck-compatible where feasible.

resources/instructions/vue.instructions.md

@@ -0,0 +1,14 @@
+---
+name: "Vue Standards"
+description: "Cross-project Vue standards for component structure, state derivation, and rendering efficiency."
+applyTo: "**/*.vue"
+---
+
+- Prefer Composition API with `<script setup>` for new components.
+- Keep components single-purpose and move reusable logic to composables.
+- Prefer computed state over watchers when deriving values.
+- Use props/events for communication instead of tight coupling.
+- Keep templates declarative; avoid embedding business logic in templates.
+- Minimize reactive dependencies and avoid broad reactive objects when narrower refs suffice.
+- Use lazy loading and route-level splitting when project architecture supports it.
+- Validate with the project's Vue lint/test/build commands.

resources/instructions/yaml.instructions.md

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+---
+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.