fix(cli): read set-profile --about from stdin when -

[Chessing234]

Summary

• buzz users set-profile --about - stored the literal - in kind:0 instead of reading stdin (unlike messages/notes).
• Resolve the - sentinel through the existing stdin helper and document it on --about.

Fixes #7162

Test plan

• printf 'multi\nline\n' | buzz users set-profile --about - publishes the full bio
• buzz users set-profile --about 'literal' still sets that string
• cargo test -p buzz-cli resolve_about_arg

[github-actions]

🔐 Codex Security Review

Status: review required for the current range.

The current range is e17a0d44c379b2ae40b91b8ba43f9a9c5bede90f...081a08b9a5b48e82336d1c09a8344b1e31cf58e4.
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