feat: CLAUDE.md with instruction on updating rule count assertion

CLAUDE.md

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+# CLAUDE.md
+
+## Project
+
+laint is an AI Agent Lint Rules SDK — a programmatic API for linting JSX/TSX code, designed to integrate with Claude Code via PostToolUse hooks.
+
+## Commands
+
+- `npm run build` — compile TypeScript + fix ESM imports
+- `npm test` — run vitest
+- `npm run lint` — eslint + prettier check
+- `npm run lint:fix` — auto-fix lint + formatting
+- `npm run knip` — dead code detection
+
+## Architecture
+
+- `src/parser.ts` — Babel parser wrapper (JSX + TypeScript)
+- `src/index.ts` — main API: `lintJsxCode()`, `getAllRuleNames()`
+- `src/rules/` — individual lint rules, each a `RuleFunction(ast, code) => LintResult[]`
+- `src/types.ts` — type definitions (`RuleFunction`, `LintResult`, etc.)
+- `src/rules/index.ts` — rule registry (maps rule names to functions)
+- `src/cli.ts` — CLI entry point (`laint init`, `laint check`)
+- `src/cli/check.ts` — file mode and hook mode linting
+- `src/cli/init.ts` — sets up `.claude/settings.json` PostToolUse hook
+
+## Adding a new rule
+
+1. Create `src/rules/my-rule.ts` exporting a `RuleFunction`
+2. Register it in `src/rules/index.ts`
+3. Create `tests/my-rule.test.ts`
+4. **Update the rule count assertion in `tests/config-modes.test.ts`** — the `getAllRuleNames` test has `expect(ruleNames.length).toBe(...)` that must match the total number of registered rules
+5. **Document the rule in `README.md`** — CI checks that every registered rule name appears in the README
+6. Run `npm test` to verify
+
+## Code style
+
+- Strict TypeScript, ESM modules
+- Prettier: 2 spaces, 100 char width, trailing commas, single quotes
+- No unnecessary type assertions — use Babel's type system directly