Register issue command in CLI

- Import and register createIssueCommand in main CLI index
- Makes 'tangled issue create' command available to users

The issue command is now fully functional and ready for testing.

Co-Authored-By: Claude Sonnet 4.5 <[e-mail]>

src/index.ts

···
 import { createAuthCommand } from './commands/auth.js';
 import { createConfigCommand } from './commands/config.js';
 import { createContextCommand } from './commands/context.js';
+import { createIssueCommand } from './commands/issue.js';
 import { createSshKeyCommand } from './commands/ssh-key.js';
 
 // Get package.json for version
···
 program.addCommand(createSshKeyCommand());
 program.addCommand(createConfigCommand());
 program.addCommand(createContextCommand());
+program.addCommand(createIssueCommand());
 
 program.parse(process.argv);