Configurable email routing for system-generated notifications

System-generated emails (vendor questionnaire reminders, task assignments, scan results, etc.) currently go to a fixed recipient. Customers — especially MSPs managing multiple clients — need to control which email address receives which type of notification. A reseller may want vendor questionnaire emails routed to the client's compliance officer, while scan alerts go to their own SOC team.

Proposed Solution:

1. Add a notification routing configuration in Settings where the admin can define recipient email addresses per notification type (e.g. scan results → soc@company.com, vendor questionnaires → compliance@client.com).
2. Support multiple recipients per notification type.
3. Allow per-client overrides for reseller/MSP accounts managing multiple orgs.
4. Include a test email function so admins can verify routing before going live.

Acceptance Criteria:

1. Admin can configure recipient email addresses per notification type.
2. Multiple recipients are supported per type.
3. Reseller accounts can set per-client overrides.
4. A test email function is available.
5. Changes take effect immediately without requiring a platform restart.