chore: add cross-tool AI config files (AGENTS.md, .cursorrules, copilot-instructions.md)

Add tool-agnostic AI coding assistant configurations so contributors
using any AI tool (Cursor, GitHub Copilot, Codex, etc.) can
automatically load project conventions.

- AGENTS.md: comprehensive tool-neutral conventions
- .cursorrules: Cursor AI compact rules
- .github/copilot-instructions.md: GitHub Copilot instructions

All content derived from CLAUDE.md to ensure consistency.

[3/3] AI tool settings exposure series

Author: kimyouknow

.cursorrules

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+# react-simplikit Cursor Rules
+
+## Project
+
+React hooks/components library. Monorepo: `packages/core` + `packages/mobile`.
+
+## Architecture
+
+Unidirectional layers: `components → hooks → utils → _internal`
+Mobile depends on core. Core must NOT depend on mobile.
+
+## Code Style
+
+- `type` over `interface` for type aliases
+- Named functions in useEffect: `useEffect(function handleResize() { ... }, [])`
+- Named exports only, no default exports
+- No `any` — strict TypeScript
+- `.js` extensions in relative imports
+- Zero runtime dependencies
+
+## SSR-Safe Pattern
+
+```ts
+const [state, setState] = useState(FIXED_INITIAL_VALUE);
+useEffect(function syncBrowserState() {
+  if (isServer()) return;
+  setState(getBrowserAPI());
+}, []);
+```
+
+## Hook Returns
+
+- 1 value → direct return
+- 2 values → tuple `[state, action]`
+- 3+ values → object `{ a, b, c }`
+
+## Testing
+
+- 100% coverage (Vitest)
+- SSR tests required for browser API hooks (`.ssr.test.ts`)
+- Use `renderHookSSR.serverOnly()` for SSR tests
+
+## File Structure
+
+Each hook in own folder: `src/hooks/useHookName/`
+- `index.ts`, `useHookName.ts`, `useHookName.spec.ts`, `useHookName.ssr.test.ts`
+- Docs: `useHookName.md` + `ko/useHookName.md`
+
+## JSDoc
+
+Required tags: `@description`, `@param`, `@returns`, `@example`
+
+## Commits
+
+Format: `<type>(<scope>): <description>`
+Types: feat, fix, docs, chore, refactor, test

.github/copilot-instructions.md

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+# Copilot Instructions for react-simplikit
+
+## Quick Reference
+
+- Monorepo: `packages/core` (react-simplikit) + `packages/mobile` (@react-simplikit/mobile)
+- Architecture: `components → hooks → utils → _internal` (unidirectional, no circular imports)
+- Mobile depends on core; core must NOT depend on mobile
+
+## Code Style Rules
+
+- Use `type` not `interface` for type aliases
+- Named functions in useEffect: `useEffect(function handleResize() { ... }, [])`
+- No default exports — named exports only
+- No `any` types — strict TypeScript
+- Include `.js` in relative imports for ESM
+
+## SSR-Safe Pattern (CRITICAL)
+
+All browser API access must use this pattern:
+
+```ts
+const [state, setState] = useState(FIXED_INITIAL_VALUE);
+useEffect(function syncBrowserState() {
+  if (isServer()) return;
+  setState(getBrowserAPI());
+}, []);
+```
+
+Never call browser APIs during state initialization.
+
+## Hook Return Values
+
+- 1 value → return directly: `useDebounce<T>(value, delay): T`
+- 2 values → tuple: `useToggle(init): [boolean, () => void]`
+- 3+ values → object: `usePagination(): { page, nextPage, prevPage }`
+
+## Testing
+
+- 100% coverage required (Vitest)
+- SSR test required for browser API hooks:
+  ```ts
+  import { renderHookSSR } from '../utils/renderHookSSR';
+  it('is safe on server side rendering', () => {
+    const result = renderHookSSR.serverOnly(() => useHookName());
+    expect(result.current).toBeDefined();
+  });
+  ```
+
+## JSDoc Template
+
+Every public API requires:
+
+```ts
+/**
+ * @description Brief description of what it does
+ * @param paramName - Parameter description
+ * @returns What the hook/function returns
+ * @example
+ * ```ts
+ * const value = useHookName(param);
+ * ```
+ */
+```
+
+## File Structure
+
+```
+src/hooks/useHookName/
+├── index.ts               # Re-export
+├── useHookName.ts         # Implementation
+├── useHookName.spec.ts    # Tests
+├── useHookName.ssr.test.ts # SSR tests
+├── useHookName.md         # English docs
+└── ko/useHookName.md      # Korean docs
+```

AGENTS.md

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+# AGENTS.md
+
+> Tool-agnostic project conventions for AI coding assistants.
+> For Claude Code-specific instructions, see [CLAUDE.md](./CLAUDE.md).
+
+## Project Overview
+
+React utility hooks/components library. Monorepo with two packages:
+- `react-simplikit` (`packages/core`) — Platform-independent React hooks & components
+- `@react-simplikit/mobile` (`packages/mobile`) — Mobile web utilities (viewport, keyboard, layout)
+
+## Architecture
+
+Layer dependency is **unidirectional** — no upward or circular imports:
+
+```
+components → hooks → utils → _internal
+```
+
+- Components may use hooks, utils, _internal
+- Hooks may use utils, _internal
+- Utils may use _internal only
+- Mobile may depend on core; core must NOT depend on mobile
+
+## File Structure
+
+Each hook/component/util lives in its own folder with co-located docs:
+
+```
+src/hooks/useHookName/
+├── index.ts               # Re-export
+├── useHookName.ts         # Implementation
+├── useHookName.spec.ts    # Tests (core) / useHookName.test.ts (mobile)
+├── useHookName.ssr.test.ts # SSR safety tests
+├── useHookName.md         # English docs
+└── ko/
+    └── useHookName.md     # Korean docs
+```
+
+## Coding Standards
+
+- **`type` over `interface`** — Always use `type` for type aliases
+- **Named functions in useEffect** — `useEffect(function handleResize() { ... }, [])` not arrow functions
+- **Strict boolean checks** — `value !== undefined` not `if (value)`
+- **Import extensions** — Include `.js` in relative imports for ESM compliance
+- **Named exports only** — No default exports
+- **No `any` types** — Full TypeScript strict mode
+- **Zero runtime dependencies**
+
+### SSR-Safe Pattern
+
+All hooks/utils accessing browser APIs must be SSR-safe:
+
+```ts
+const [state, setState] = useState(FIXED_INITIAL_VALUE);
+useEffect(function syncBrowserState() {
+  if (isServer()) return;
+  setState(getBrowserAPI());
+}, []);
+```
+
+Never initialize state with browser API calls (causes hydration mismatch).
+
+### Hook Return Value Convention
+
+- **Single value**: `useDebounce<T>(value, delay): T`
+- **Tuple** (2 items): `useToggle(init): [boolean, () => void]`
+- **Object** (3+ items): `usePagination(): { page, nextPage, prevPage }`
+
+## Testing
+
+- **100% coverage mandatory** — Enforced by Vitest coverage threshold
+- **SSR tests required** — All hooks accessing browser APIs need `.ssr.test.ts`
+- **SSR test pattern**:
+  ```ts
+  import { renderHookSSR } from '../utils/renderHookSSR';
+  it('is safe on server side rendering', () => {
+    const result = renderHookSSR.serverOnly(() => useHookName());
+    expect(result.current).toBeDefined();
+  });
+  ```
+
+## Documentation
+
+- **Bilingual**: English + Korean (co-located in hook folders)
+- **JSDoc required**: Every public API must have `@description` + `@example` + `@param` + `@returns`
+
+## Commit Convention
+
+Format: `<type>(<scope>): <description>`
+
+Types: `feat`, `fix`, `docs`, `chore`, `refactor`, `test`
+Scope: `core`, `mobile`, or area name
+
+## Commands
+
+```bash
+yarn build          # Build all packages (tsup)
+yarn test           # Run tests (Vitest)
+yarn fix            # Auto-fix lint + format
+yarn typecheck      # Type check (tsc --noEmit)
+```