Add construct config section migration hint

[edwin-zvs]

Summary

• Expand legacy migration copy/paste guidance with a safe config rewrite command for adapter section renames.
• Updates migration snippet to convert legacy adapter table names from adapters.zarvis to adapters.smith.
• Update unit coverage in legacy_migration_notice_includes_detected_items.

Verification

• cargo fmt --all
• cargo test -p agentd legacy_migration_notice_includes_detected_items -- --nocapture