Add Linear CLI commands: me and my-issues

[crogger62]

Two quick CLI apps that tell you:

1. me.ts - who the current user is. run npm run me
2. myIssues.ts- listing all of the issues assigned to the current user. run npm run my-issues

• Adds npm run me and npm run my-issues
• Adds shared client helper at linearClient.ts for .env loading and LINEAR_API_KEY validation
• Updates .gitignore to ignore .env
• Includes required dependencies/scripts in root package.json
• Verified locally by running both commands successfully

[crogger62]

quick test steps:
npm install
npm run me
npm run my-issues

[blkinney]

@crogger62 What's the use case for this?