build(deps): bump fastify from 5.5.0 to 5.6.0 in /backend

Bumps [fastify](https://github.com/fastify/fastify) from 5.5.0 to 5.6.0.
- [Release notes](https://github.com/fastify/fastify/releases)
- [Commits](https://github.com/fastify/fastify/compare/v5.5.0...v5.6.0)

---
updated-dependencies:
- dependency-name: fastify
  dependency-version: 5.6.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

backend/package-lock.json

@@ -12,7 +12,7 @@
         "@fastify/type-provider-typebox": "^5.2.0",
         "@types/jest": "^30.0.0",
         "@types/nodemailer": "^7.0.1",
-        "fastify": "^5.5.0",
+        "fastify": "^5.6.0",
         "nodemailer": "^7.0.5",
         "ts-dotenv": "^0.9.1"
       },
@@ -5949,9 +5949,9 @@
       }
     },
     "node_modules/fastify": {
-      "version": "5.5.0",
+      "version": "5.6.0",
-      "resolved": "https://registry.npmjs.org/fastify/-/fastify-5.5.0.tgz",
+      "resolved": "https://registry.npmjs.org/fastify/-/fastify-5.6.0.tgz",
-      "integrity": "sha512-ZWSWlzj3K/DcULCnCjEiC2zn2FBPdlZsSA/pnPa/dbUfLvxkD/Nqmb0XXMXLrWkeM4uQPUvjdJpwtXmTfriXqw==",
+      "integrity": "sha512-9j2r9TnwNsfGiCKGYT0Voqy244qwcoYM9qvNi/i+F8sNNWDnqUEVuGYNc9GyjldhXmMlJmVPS6gI1LdvjYGRJw==",
       "funding": [
         {
           "type": "github",

backend/package.json

@@ -43,7 +43,7 @@
     "@fastify/type-provider-typebox": "^5.2.0",
     "@types/jest": "^30.0.0",
     "@types/nodemailer": "^7.0.1",
-    "fastify": "^5.5.0",
+    "fastify": "^5.6.0",
     "nodemailer": "^7.0.5",
     "ts-dotenv": "^0.9.1"
   },