feat(backend): #28 templates email validation compte (Handlebars)

- Templates .hbs parent principal, co-parent, AM + lien create-password
- app_name / app_url / expéditeur via ConfigService (sendEmail)
- validateUser: renouvelle token création MDP + envoi email si sans password
- Dist: assets *.hbs (nest-cli)
- Tests unitaires MailService (mock sendEmail)
- Doc liste tickets #28 terminé

Made-with: Cursor

backend/nest-cli.json

@@ -3,6 +3,12 @@
   "collection": "@nestjs/schematics",
   "sourceRoot": "src",
   "compilerOptions": {
-    "deleteOutDir": true
+    "deleteOutDir": true,
+    "assets": [
+      {
+        "include": "**/*.hbs",
+        "watchAssets": true
+      }
+    ]
   }
 }