Initial commit: OpenFUT Core

Offline Ultimate Team backend — game-independent REST API.

- 19 API endpoints: auth, profiles, clubs, cards, packs, squads,
  objectives, SBCs, match rewards, NPC market, statistics
- Axum + SQLite + SQLx with full migrations
- Weighted pack generator, SBC validation engine
- JSON-driven mod data (cards, packs, objectives, SBCs)
- 5 integration tests passing

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/error.rs

@@ -0,0 +1,62 @@
+use axum::{
+    http::StatusCode,
+    response::{IntoResponse, Response},
+    Json,
+};
+use serde_json::json;
+use thiserror::Error;
+
+#[derive(Debug, Error)]
+pub enum AppError {
+    #[error("not found: {0}")]
+    NotFound(String),
+
+    #[error("bad request: {0}")]
+    BadRequest(String),
+
+    #[error("conflict: {0}")]
+    Conflict(String),
+
+    #[error("database error: {0}")]
+    Database(#[from] sqlx::Error),
+
+    #[error("internal error: {0}")]
+    Internal(#[from] anyhow::Error),
+
+    #[error("io error: {0}")]
+    Io(#[from] std::io::Error),
+
+    #[error("json error: {0}")]
+    Json(#[from] serde_json::Error),
+}
+
+impl IntoResponse for AppError {
+    fn into_response(self) -> Response {
+        let (status, message) = match &self {
+            AppError::NotFound(msg) => (StatusCode::NOT_FOUND, msg.clone()),
+            AppError::BadRequest(msg) => (StatusCode::BAD_REQUEST, msg.clone()),
+            AppError::Conflict(msg) => (StatusCode::CONFLICT, msg.clone()),
+            AppError::Database(e) => {
+                tracing::error!("Database error: {e}");
+                (StatusCode::INTERNAL_SERVER_ERROR, "database error".into())
+            }
+            AppError::Internal(e) => {
+                tracing::error!("Internal error: {e}");
+                (
+                    StatusCode::INTERNAL_SERVER_ERROR,
+                    "internal server error".into(),
+                )
+            }
+            AppError::Io(e) => {
+                tracing::error!("IO error: {e}");
+                (StatusCode::INTERNAL_SERVER_ERROR, "io error".into())
+            }
+            AppError::Json(e) => (StatusCode::BAD_REQUEST, format!("json parse error: {e}")),
+        };
+
+        let body = Json(json!({ "error": message }));
+        (status, body).into_response()
+    }
+}
+
+pub type AppResult<T> = Result<T, AppError>;