feat: Implement initial backend structure with API, WebSocket, core models, services, and documentation, alongside dependency and gitignore updates.

Cargo.toml

@@ -9,6 +9,7 @@ actix-rt = "2.11.0"
 actix-web = "4.11.0"
 actix-web-actors = "4.3.0"
 actix-web-lab = "0.24.3"
+actix-cors = "0.7"
 awc = "3.8.1"
 serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"
@@ -24,3 +25,4 @@ utoipa = { version = "4", features = ["actix_extras"] }
 utoipa-swagger-ui = { version = "4", features = ["actix-web"] }
 validator = { version = "0.16", features = ["derive"] }
 jsonwebtoken = "9"
+dotenv = "0.15"