feat: Implement unsubscribe link for marketing automation [31188f42]

This commit introduces a new unsubscribe feature to allow contacts to opt-out
from marketing automation.

Key changes include:
- Database schema migration: Added  (UUID) to the  model.
- Data population: Implemented a script to assign unique tokens to existing contacts.
- API endpoint: Created a public GET  endpoint to handle opt-out requests.
- Automation: New contacts automatically receive an unsubscribe token upon creation.
- Integration: The full unsubscribe link is now returned via the provisioning API
  for storage in SuperOffice UDFs (ProgID: SuperOffice:9).
- Documentation: Updated  and
  to reflect the new feature and its integration requirements.
- Added  for quick overview and next steps.

SUPEROFFICE_INTEGRATION_PLAN.md

@@ -63,6 +63,7 @@ Folgende Felder sollten am Objekt `Company` (bzw. `Contact` in SuperOffice-Termi
 | `AI Summary` | Text (Long/Memo) | Kurze Zusammenfassung der Analyse |
 | `AI Last Update` | Date | Zeitstempel der letzten Anreicherung |
 | `AI Status` | List/Select | Pending / Enriched / Error |
+| `Unsubscribe-Link` | Text/Link | **NEU:** Speichert den personalisierten Link zur Abmeldung von der Marketing-Automation. (ProgID: SuperOffice:9) |
 
 ### Benötigtes Feld im Company Explorer
 | Feldname | Typ | Zweck |