fix(cli): capitalize the first characters of cli help texts and fix minor grammar errors

[bearomorphism]

As title.

Why

Most of cli tools, like git, uv, have their commands' help text with first character capital. Maybe we should follow the convention?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.88%. Comparing base (1d89195) to head (34027e8).
⚠️ Report is 2 commits behind head on master.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1776   +/-   ##
=======================================
  Coverage   97.88%   97.88%           
=======================================
  Files          60       60           
  Lines        2606     2606           
=======================================
  Hits         2551     2551           
  Misses         55       55           

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