fix: restore corrupted JSDoc and function signature in subAgent.js

[avoidwork]

Description

Restored the corrupted JSDoc return type annotation and function signature for executeFanOut in src/tools/subAgent.js. A previous PR had injected code into the JSDoc comment, breaking the function definition.

Type of Change

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactor (no functional changes)
• Performance improvement
• CI / build / tooling

Testing

Verified the file reads correctly after the patch. The function signature and JSDoc are now properly structured.

Coverage

• Line coverage maintained

Checklist

• npm run lint passes
• Tests pass with maintained line coverage
• No forbidden patterns used
• Conventional Commit style applied