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/location-history.md

@@ -4,22 +4,37 @@
 
 ## Diagramme
 
-```mermaid
-erDiagram
-    USERS ||--o{ LOCATION_HISTORY : "génère"
+```kroki-dbml
+Table users {
+  id uuid [primary key]
+}
 
-    LOCATION_HISTORY {
-        uuid id PK
-        uuid user_id FK
-        geography location
-        string geohash
-        boolean anonymized
-        string context
-        float speed_kmh
-        float accuracy_meters
-        timestamp created_at
-        timestamp anonymized_at
-    }
+Table location_history {
+  id uuid [primary key]
+  user_id uuid [not null, ref: > users.id]
+  location geography [note: 'PostGIS geography type: POINT with SRID 4326 (WGS84)']
+  geohash varchar(12) [note: 'Precision 5 geohash (~5km²) after anonymization']
+  anonymized boolean [not null, default: false, note: 'true after 24h auto-anonymization']
+  context location_context_enum [not null]
+  speed_kmh float [note: 'GPS speed in km/h (NULL if stationary)']
+  accuracy_meters float [not null, note: 'GPS accuracy radius in meters']
+  created_at timestamp [not null, default: `now()`]
+  anonymized_at timestamp [note: 'When precise location was replaced by geohash']
+
+  indexes {
+    (user_id, created_at) [note: 'User location timeline']
+    (created_at, anonymized) [note: 'Daily anonymization job (WHERE anonymized = false AND created_at < NOW() - 24h)']
+    (location) [type: gist, note: 'PostGIS spatial index for proximity queries']
+    (geohash) [note: 'Analytics queries on anonymized data']
+  }
+}
+
+Enum location_context_enum {
+  listening [note: 'Position pendant écoute de contenu']
+  search [note: 'Position lors d une recherche']
+  background [note: 'Tracking en arrière-plan']
+  manual [note: 'Position partagée manuellement']
+}
 ```
 
 ## Légende