feat: show relay-hosted agents in Agents tab

[sapience7-hub]

Summary

Buzz already discovers relay-hosted agent profiles, but the Agents tab only rendered locally managed agents and personas. This adds a Remote agents section that shows discovered relay agents with status, model/type, avatar fallback, and profile navigation.

It also adds buzz agents publish-profile so a headless agent can publish a kind 10100 relay-visible profile with its public metadata, capabilities, status, and response policy.

Implementation notes

• Relay agent profiles are already discovered through the existing relay-agent query; the UI now renders those records instead of omitting them.
• Remote cards reuse the existing identity/profile panel and avatar fallback.
• publish-profile validates status and aligned channel metadata before signing and submitting the profile event.
• The Tauri release build validates external sidecars; the existing sidecar build process must run before packaging.

Validation

• cargo check -p buzz-cli
• cargo test -p buzz-cli — 274 passed, 1 ignored
• Biome check for the changed desktop files
• git diff --check
• Windows x64 desktop build completed successfully and produced MSI and NSIS installers.

The repository pre-commit/pre-push hooks currently fail before running their checks because upstream main has an unrelated Justfile parse error at line 68; the focused checks above pass.