feat: support context length shorthand

[puneetdixit200]

Summary

• add parsing for --context-length values like 64k and 128k
• apply the parser to ranking, plan, upgrade, and run commands
• document shorthand usage in the CLI reference

Closes #59.

Verification

• .venv/bin/python -m pytest tests/test_cli.py -q -> 32 passed
• .venv/bin/python -m pytest -q -> 195 passed

AI-assisted work

This patch was prepared with AI assistance and manually reviewed. The targeted tests were written first, observed failing before implementation, then the full test suite was run locally.

[Andyyyy64]

Thanks for working on this.

I’m going to close this one in favor of #64, which covers the same issue and keeps the parsing logic in a reusable CLI parameter type.

I do appreciate the docs updates here. I’ll make sure the final version keeps the CLI docs covered as well.