Add ESLint configuration with TypeScript support for code quality enforcement

[Copilot]

This PR sets up comprehensive linting for the tiger-linear-mcp-server project using ESLint with TypeScript support and reasonable default rules.

Changes Made

ESLint Configuration (.eslintrc.mjs)

• Modern flat config format with TypeScript parser integration
• TypeScript-specific rules for type safety and best practices
• Import/export rules enforcing ES module patterns with .js extensions
• Code quality rules aligned with existing project guidelines from CLAUDE.md
• Integration with Prettier to avoid formatting conflicts

Package Configuration

• Added ESLint dependencies: eslint, @typescript-eslint/parser, @typescript-eslint/eslint-plugin, eslint-plugin-import
• Added three lint scripts:
  • npm run lint - Check for linting issues
  • npm run lint:fix - Auto-fix issues where possible
  • npm run lint:check - Zero warnings mode for CI/CD

Supporting Files

• .eslintignore - Excludes appropriate directories (node_modules, dist, shared boilerplate, etc.)
• Updated .gitignore to exclude ESLint cache files
• Enhanced CLAUDE.md with linting documentation and usage instructions

Key Features

The ESLint configuration enforces the project's established coding standards:

• ES Modules: Enforces .js extensions in import paths while allowing .ts source files
• TypeScript: Strict type checking with sensible defaults (warns on any, catches unused variables)
• Async Patterns: Prefers async/await over Promise chains per project guidelines
• Import Ordering: Groups external dependencies first, then internal modules
• Naming Conventions: Enforces camelCase for variables/functions, allows console logging for MCP server debugging
• Code Quality: Strict equality (===), proper variable declarations (const over let/var)

Usage

After merging, developers can:

npm install           # Install ESLint dependencies
npm run lint          # Check existing code for issues
npm run lint:fix      # Auto-fix formatting and simple issues
npm run lint:check    # CI mode with zero warnings tolerance

The configuration is specifically tailored to this project's TypeScript + ES modules architecture and integrates seamlessly with the existing Prettier setup.

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