docs: add descriptive comments to command examples (gh CLI style)

[q-soriarty]

Problem

The gh CLI manual shows examples with descriptive comments:

# Close issue
$ gh issue close 123

# Close issue and add a closing comment
$ gh issue close 123 --comment "Closing this issue"

Our examples only have the bare commands without comments:

$ copia issue close 12
$ copia issue close 12 --comment "Fixed in PR #7"

Fix

Update the Example field in each Cobra command definition to include # comment lines explaining what each example does. The gen-docs.go script already preserves # comments.

Scope

All commands with examples (~30 files in pkg/cmd/).

Reference

https://cli.github.com/manual/gh_issue_close

[q-soriarty]

Superseded by #132 (Jekyll documentation migration). Will be closed when #132 is merged.

[github-actions]

Closed by #136 (merged into develop).