comment: expose edit/resolve (client.UpdateTaskComment exists but is unused)

[timimsms]

Context

The API client already supports editing a comment's text and resolving it, but no CLI command exposes this. Users can comment add, comment list, and comment delete, but cannot edit or resolve comments without dropping down to raw cu api calls.

Evidence

• internal/api/client.go:525-526 — Client.UpdateTaskComment(ctx, commentID, text, resolved) exists and handles both text updates and the resolved flag.
• internal/cmd/comment.go — no subcommand calls UpdateTaskComment.

Suggested fix

Add two subcommands:

• cu comment edit <comment-id> -m "new text" — update comment text.
• cu comment resolve <comment-id> — set resolved (consider --undo to unresolve).

Both map directly onto the existing UpdateTaskComment client method.