Cleanup: Several api/ files missing trailing newlines

[gkorland]

Description

The following files under api/ are missing POSIX-required trailing newlines:

• api/analyzers/csharp/__init__.py
• api/entities/entity.py
• api/index.py
• api/llm.py
• api/prompts.py

This can cause issues with some tools and produces noisy git diffs.

Suggested Fix

Add a trailing newline to each file. Most editors can be configured to do this automatically.

Context

Found during code review of PR #522.