Implement explanation of a specific file from the local directory

[calchiwo]

Right now explainthisrepo supports repository and directory analysis:

explainthisrepo owner/repo
explainthisrepo .
explainthisrepo ./path/to/directory

So I have this idea to implement specific file analysis in local director

For example:

explainthisrepo ./[main.py](http://main.py/)
explainthisrepo ./[build.js](http://build.js/)
explainthisrepo ./Dockerfile

Behavior:

• Detect when the target is a file (os.path.isfile)

• Read file contents

• Generate an explanation for the file

Prompt example:

Explain what this file does and how it works.

<file contents>

Flag behavior:

Flag	Supported
--quick	✓
--simple	✓
--detailed	✓
--stack	✗ (repo-only)

If --stack is used on a file:

error: stack detection requires a repository or directory

This would make ExplainThisRepo useful for quickly understanding individual files.