chore: normalize line endings (CRLF -> LF)

No content changes: git diff --ignore-all-space over these files is empty.
The churn came from editing on Windows against a repo checked out with LF.

backend/.env.example

@@ -1,8 +1,8 @@
-# Port to serve the application on the host (routed via Nginx)
-APP_PORT=8000
-
-# GPU index to allocate (e.g. 0, 1, or 0,1)
-CUDA_VISIBLE_DEVICES=1
-
-# Secret used to sign/verify account login JWTs
-JWT_SECRET=change-me
+# Port to serve the application on the host (routed via Nginx)
+APP_PORT=8000
+
+# GPU index to allocate (e.g. 0, 1, or 0,1)
+CUDA_VISIBLE_DEVICES=1
+
+# Secret used to sign/verify account login JWTs
+JWT_SECRET=change-me