docs: migrer schémas BDD de Mermaid vers DBML

Remplace les diagrammes Mermaid par DBML (via kroki-dbml) pour
une meilleure expressivité des schémas de base de données :
- Ajout support notes, contraintes et indexes détaillés
- Migration de tous les schémas d'entités partagées
- Ajout fichier exemple dbml-example.md
- Configuration plugin mkdocs-kroki pour rendu DBML

docs/domains/_shared/entities/exports.md

@@ -4,22 +4,43 @@
 
 ## Diagramme
 
-```mermaid
-erDiagram
-    USERS ||--o{ DATA_EXPORTS : "demande"
+```kroki-dbml
+Table users {
+  id uuid [primary key]
+}
 
-    DATA_EXPORTS {
-        uuid id PK
-        uuid user_id FK
-        string status
-        string export_url
-        bigint size_bytes
-        string format
-        timestamp requested_at
-        timestamp generated_at
-        timestamp expires_at
-        timestamp downloaded_at
-    }
+Table data_exports {
+  id uuid [primary key]
+  user_id uuid [not null, ref: > users.id]
+  status export_status_enum [not null, default: 'pending']
+  export_url varchar(512) [note: 'S3/CDN signed URL (NULL until generated)']
+  size_bytes bigint [note: 'File size in bytes (NULL until generated)']
+  format export_format_enum [not null, default: 'json']
+  requested_at timestamp [not null, default: `now()`]
+  generated_at timestamp [note: 'When export file was created (NULL if pending/generating)']
+  expires_at timestamp [note: 'Auto-calculated: generated_at + 7 days']
+  downloaded_at timestamp [note: 'First download timestamp (NULL if not yet downloaded)']
+
+  indexes {
+    (user_id, requested_at) [note: 'User export history']
+    (status, requested_at) [note: 'Background worker queue (WHERE status = pending)']
+    (expires_at) [note: 'Daily cleanup job (DELETE WHERE expires_at < NOW())']
+  }
+}
+
+Enum export_status_enum {
+  pending [note: 'Demande en file d attente']
+  generating [note: 'Génération en cours (worker background)']
+  ready [note: 'Export disponible au téléchargement']
+  downloaded [note: 'Export téléchargé par l utilisateur']
+  expired [note: 'Export expiré (supprimé automatiquement)']
+}
+
+Enum export_format_enum {
+  json [note: 'Machine-readable (données brutes)']
+  html [note: 'Human-readable (page web stylée)']
+  zip [note: 'Archive complète (JSON + HTML + audio files)']
+}
 ```
 
 ## Légende