Fixes #2534.

What changed

• Added an SDK profile builder that overlays Buzz-owned fields onto the complete existing kind:0 object.
• Updated buzz users set-profile to preserve name and every unmodeled field instead of rebuilding from a five-key allowlist.
• Updated Desktop profile edits to merge into the raw current profile object.
• Updated automatic managed-agent profile sync to read the existing kind:0 before publishing a rename/avatar change.
• Added regression coverage for bot, website, lud16, nip05, and other passthrough metadata.

Root cause

Kind 0 is a replaceable event, but Buzz's builders created a new JSON object containing only display_name, name, picture, about, and nip05. Every omitted key was therefore deleted on the relay. The managed-agent path was especially destructive because it automatically published only display_name and picture.

The CLI also promoted a stored name into display_name when no display name existed, while deleting the original name key.

User impact

Profile edits and automatic agent reconciliation now preserve metadata created by other Nostr clients and future NIPs. In particular, Buzz no longer silently removes the NIP-24 bot: true disclosure, NIP-05 identity, website, banner, Lightning address, or unknown extension fields.

If the existing profile cannot be queried, managed-agent synchronization fails safely instead of publishing a destructive partial replacement.

Validation

• cargo fmt --all
• cargo fmt --manifest-path desktop/src-tauri/Cargo.toml
• 5 Buzz SDK profile tests passed
• cargo check -p buzz-cli
• 21 Desktop profile-related tests passed