Add utoipa and Scalar for API documentation

- Add utoipa and utoipa-scalar dependencies
- Add ToSchema derives to all models
- Add OpenAPI path annotations to auth, users, and health handlers
- Create openapi.rs module with API documentation
- Serve Scalar UI at /docs endpoint
- Include JWT bearer auth security scheme

Co-Authored-By: Warp <agent@warp.dev>

src/models/user.rs

@@ -1,9 +1,10 @@
 use chrono::{DateTime, Utc};
 use serde::{Deserialize, Serialize};
 use sqlx::FromRow;
+use utoipa::ToSchema;
 
 /// User model representing the users table
-#[derive(Debug, Clone, Serialize, Deserialize, FromRow)]
+#[derive(Debug, Clone, Serialize, Deserialize, FromRow, ToSchema)]
 pub struct User {
     pub id: i32,
     pub date_registered: DateTime<Utc>,
@@ -25,7 +26,7 @@ pub struct User {
 }
 
 /// User public profile (without sensitive data)
-#[derive(Debug, Clone, Serialize)]
+#[derive(Debug, Clone, Serialize, ToSchema)]
 pub struct UserProfile {
     pub id: i32,
     pub date_registered: DateTime<Utc>,
@@ -57,7 +58,7 @@ impl From<User> for UserProfile {
 }
 
 /// Create user request (internal use)
-#[derive(Debug, Deserialize)]
+#[derive(Debug, Deserialize, ToSchema)]
 pub struct CreateUser {
     pub firstname: String,
     pub lastname: String,
@@ -67,7 +68,7 @@ pub struct CreateUser {
 }
 
 /// Update user request
-#[derive(Debug, Deserialize)]
+#[derive(Debug, Deserialize, ToSchema)]
 pub struct UpdateUser {
     pub firstname: Option<String>,
     pub lastname: Option<String>,
@@ -76,7 +77,7 @@ pub struct UpdateUser {
 }
 
 /// Player stats response
-#[derive(Debug, Clone, Serialize)]
+#[derive(Debug, Clone, Serialize, ToSchema)]
 pub struct PlayerStats {
     pub id: i32,
     pub username: String,