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/package.json

@@ -36,6 +36,7 @@
     "bcryptjs": "^3.0.2",
     "class-transformer": "^0.5.1",
     "class-validator": "^0.14.2",
+    "handlebars": "^4.7.8",
     "joi": "^18.0.0",
     "mapped-types": "^0.0.1",
     "multer": "^1.4.5-lts.1",
@@ -55,6 +56,7 @@
     "@nestjs/testing": "^11.0.1",
     "@types/bcrypt": "^6.0.0",
     "@types/express": "^5.0.0",
+    "@types/handlebars": "^4.1.0",
     "@types/jest": "^30.0.0",
     "@types/multer": "^1.4.12",
     "@types/node": "^22.10.7",