fix: correct variable reference in parameter parsing logic

[ayakut16]

Description

See #10 for details
Fixes #10

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

By running the tool locally:

1. echo "Hello, World" > ~/file.txt
2. make setup & ./bin/mcp shell npx -y @modelcontextprotocol/server-filesystem ~
3. call read_file -p {"path":"~/file.txt"}

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
  --> Unfortunately, this is not possible with the current unit test setup, because the test reimplements the logic instead of using the actual implementation for this particular case.
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[f]

🚀 Thank you!