Add 1Password-backed auth vault profiles

[Stanzilla]

Summary

• add 1Password-backed auth vault profiles with a recommended item-based flow via the onepassword-item and onepassword-vault flags
• resolve username, password, and optional OTP values locally at auth login time through the 1Password CLI
• keep username-op, password-op, and otp-op as advanced fallbacks for partial or custom 1Password setups and second factors handled outside 1Password such as SMS or email
• update CLI help, docs, skills, and tests to cover the new auth flow

Testing

• cargo fmt -- --check
• cargo test -q
• cargo clippy -q

Closes #711.

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