fix: propagate campaign execution errors + fix-campaign-seeds

[scharissis]

Fixes silent error swallowing in campaign execution.

The tokio::select! block was discarding errors by binding the result to _. When execute_stage returned an error (e.g., MinBalanceInsufficient when default min-balance is too low), the campaign would silently exit with "Campaign completed" instead of showing the error.

[zeroXbrock]

absorbing #419 with this

[zeroXbrock]

great work, thank you @bitwiseguy @scharissis!