Add non-interactive --repo and --skill options to remove command

[Copilot]

The remove command was interactive-only, requiring a checkbox prompt even when the target repo or skill was already known.

Changes

• skillup/cli.py

  • Extracted _remove_skill() helper to deduplicate filesystem removal + lock update logic
  • Added --repo option: removes all skills from a tracked repo without prompting
  • Added --skill/-s option (repeatable, requires --repo): removes one or more specific skills non-interactively
  • Interactive checkbox mode preserved when no options are provided

• tests/test_remove.py — new test module covering all non-interactive paths: full-repo removal, single/multi-skill removal, unknown repo/skill errors, and filesystem directory cleanup

• README.md — updated "Remove skills" section with all three usage modes

Usage

skillup remove                                         # interactive (unchanged)
skillup remove --repo owner/repo                       # remove entire repo
skillup remove --repo owner/repo --skill pdf           # remove one skill
skillup remove --repo owner/repo --skill pdf --skill summarize  # remove multiple