refactor: use stderr for CLI error output

[sanjana2505006]

I noticed that the CLI was printing error messages (like invalid arguments or config load failures) to stdout, which isn't ideal for scripting or standard error handling. This PR redirects those critical errors to stderr.

I also enhanced the PrintUsage function to accept an output stream, so -h/--help still goes to stdout (as expected), but incorrect usage warnings go to stderr. The usage message itself has been slightly polished for better readability.

Changes:

• PrintUsage now takes an optional std::ostream& argument (defaults to cout).
• Invalid command-line arguments now print usage to cerr and return exit code 1.
• Config loading and logger initialization errors now print to cerr.
• Added <iostream> include for correctness.

[sanjana2505006]

@git-hulk Whenever you get a chance, please review and let me know if any changes are needed

[PragmaTwice]

maybe we can just change it to std::cerr?

[sanjana2505006]

I actually went with the std::ostream parameter because I wanted to stick to the standard way most CLI tools handle output. Usually, when someone asks for help explicitly (like with --help), they expect it on stdout so they can pipe it to grep or less. But if they just mess up a command, the usage warning should definitely go to stderr.

I also noticed that --version uses stdout right now, so this keeps things consistent.
Let me know if that makes sense! I'm happy to simplify it to just std::cerr if you'd prefer less boilerplate, but I figured this separation was worth the extra bit of code.

[sanjana2505006]

@PragmaTwice whenever you get a chance, please let me know your thoughts on this. If you still think we should just use std::cerr for simplicity, I'm happy to make that change!