Signup confirmation email never arrives (Windows, Buzz Desktop v0.5.5)

## Description
During onboarding in Buzz Desktop, the account/workspace confirmation email never arrives.

## Environment
- Buzz Desktop version: 0.5.5 (alpha-unsigned, Windows x64 installer)
- OS: Windows 11 Pro
- Install source: GitHub release `desktop-v0.5.5`

## Steps taken to rule out user error
- Checked spam/junk folder — nothing received
- Confirmed the email address entered at signup is correct and typo-free
- Installer completed successfully and the app opens normally

## Observed CLI-side symptom
Because the workspace/account was never confirmed, no relay is assigned to the identity yet. Inspecting `agents/managed-agents.json` under the app's Roaming data directory shows `"relay_url": ""` for the configured agents, so `buzz` CLI commands fail with a relay connection error (defaulting to `http://localhost:3000`) rather than a clear "workspace not yet confirmed" message.

## Expected behavior
- Confirmation email is delivered promptly, or
- The app/CLI surfaces a clear, actionable error state (e.g. "workspace pending email confirmation — resend?") instead of leaving `relay_url` empty with no explanation.

## Suggested improvements
- Add a "resend confirmation email" action in the onboarding UI
- Add a CLI/desktop diagnostic that explicitly reports "account pending confirmation" instead of a generic relay error

Start by reproducing onboarding on Windows 11 with Buzz Desktop v0.5.5, then inspect agents/managed-agents.json and trace the empty relay_url back to the confirmation state. Done means the confirmation email arrives or the desktop/CLI presents an actionable pending-confirmation or resend state instead of the generic relay error.

Written by the indexing model from the issue text.