feat(pipelines): ✨ implement azdo pipelines folder update command

[tmeckel]

Summary

Implements azdo pipelines folder update [ORG:]PROJECT/PATH, mirroring az pipelines folder update. Renames a build definition folder or changes its description.

Changes

• New command update under pipelines folder (alias u), cobra.ExactArgs(1)
• Flags: --new-path, --new-description — at least one required (util.FlagErrorf on mutex violation)
• Behavior: fetch folder via GetFolders (exact path, unique match enforced) → mutate → UpdateFolder (full replace POST, original path used as target)
• Plain output: Updated folder <path> (new path when renamed)
• JSON output: raw *build.Folder from UpdateFolder
• Unit tests: command structure, rename-only, description-only, both, mutex violation, not found, ambiguous path, API errors, JSON export, missing args
• Regenerated docs/

Fixes #266