feat: implement filament and spool preset services with CRUD operations

- Add `FilamentService` for managing filament inventory, including creation, retrieval, updating, and deletion of filaments.
- Introduce `SpoolPresetService` for handling spool presets, allowing users to create, update, and delete their custom presets.
- Create domain models for `Filament` and `SpoolPreset` with necessary fields and methods.
- Define repository interfaces for filament and spool preset persistence.
- Implement application configuration management from environment variables.
- Set up error handling with a centralized `AppError` type.
- Build the Axum router with public and protected routes for user authentication and resource management.

backend/src/error.rs

@@ -0,0 +1,78 @@
+use axum::{
+    http::StatusCode,
+    response::{IntoResponse, Response},
+    Json,
+};
+use serde_json::json;
+
+/// Erro centralizado da aplicação.
+/// Toda camada retorna `Result<T, AppError>`.
+#[derive(Debug, thiserror::Error)]
+pub enum AppError {
+    #[error("not found")]
+    NotFound,
+
+    #[error("unauthorized")]
+    Unauthorized,
+
+    #[error("forbidden")]
+    Forbidden,
+
+    #[error("validation error: {0}")]
+    Validation(String),
+
+    #[error("conflict: {0}")]
+    Conflict(String),
+
+    #[error("unprocessable entity: {0}")]
+    UnprocessableEntity(String),
+
+    #[error("internal error")]
+    Internal(#[from] anyhow::Error),
+}
+
+impl AppError {
+    fn status_and_code(&self) -> (StatusCode, &'static str) {
+        match self {
+            Self::NotFound => (StatusCode::NOT_FOUND, "NOT_FOUND"),
+            Self::Unauthorized => (StatusCode::UNAUTHORIZED, "UNAUTHORIZED"),
+            Self::Forbidden => (StatusCode::FORBIDDEN, "FORBIDDEN"),
+            Self::Validation(_) => (StatusCode::BAD_REQUEST, "VALIDATION_ERROR"),
+            Self::Conflict(_) => (StatusCode::CONFLICT, "CONFLICT"),
+            Self::UnprocessableEntity(_) => (StatusCode::UNPROCESSABLE_ENTITY, "UNPROCESSABLE_ENTITY"),
+            Self::Internal(_) => (StatusCode::INTERNAL_SERVER_ERROR, "INTERNAL_ERROR"),
+        }
+    }
+}
+
+impl IntoResponse for AppError {
+    fn into_response(self) -> Response {
+        let (status, code) = self.status_and_code();
+
+        if status == StatusCode::INTERNAL_SERVER_ERROR {
+            tracing::error!(error = %self, "Internal server error");
+        }
+
+        let body = Json(json!({
+            "error": self.to_string(),
+            "code": code,
+        }));
+
+        (status, body).into_response()
+    }
+}
+
+impl From<sqlx::Error> for AppError {
+    fn from(err: sqlx::Error) -> Self {
+        match err {
+            sqlx::Error::RowNotFound => Self::NotFound,
+            _ => Self::Internal(err.into()),
+        }
+    }
+}
+
+impl From<validator::ValidationErrors> for AppError {
+    fn from(err: validator::ValidationErrors) -> Self {
+        Self::Validation(err.to_string())
+    }
+}