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/.env.development

@@ -0,0 +1,20 @@
+# --- PostgreSQL (usado pelo Docker Compose e pela connection string abaixo) ---
+POSTGRES_HOST=localhost
+POSTGRES_PORT=5432
+POSTGRES_USER=local_user
+POSTGRES_DB=local_db
+POSTGRES_PASSWORD=local_password
+
+# --- App (lido por src/config.rs) ---
+DATABASE_URL=postgres://local_user:local_password@localhost:5432/local_db
+
+JWT_SECRET=dev-secret-change-in-production
+JWT_EXPIRY_SECS=3600
+JWT_REFRESH_EXPIRY_SECS=2592000
+
+GOOGLE_CLIENT_ID=
+GOOGLE_CLIENT_SECRET=
+
+HOST=0.0.0.0
+PORT=8080
+APP_ENV=development