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/migrations/20240101000001_create_users.sql

@@ -0,0 +1,16 @@
+-- Migration: 001 - Criar tabela de usuários
+
+CREATE EXTENSION IF NOT EXISTS "uuid-ossp";
+
+CREATE TABLE users (
+    id              UUID PRIMARY KEY DEFAULT uuid_generate_v4(),
+    email           TEXT NOT NULL UNIQUE,
+    password_hash   TEXT,
+    google_id       TEXT UNIQUE,
+    email_verified  BOOLEAN NOT NULL DEFAULT FALSE,
+    created_at      TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at      TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+CREATE INDEX idx_users_email    ON users (email);
+CREATE INDEX idx_users_google_id ON users (google_id) WHERE google_id IS NOT NULL;

backend/migrations/20240101000002_create_spool_presets.sql

@@ -0,0 +1,30 @@
+-- Migration: 002 - Criar tabela de presets de carretel e inserir presets do sistema
+
+CREATE TABLE spool_presets (
+    id              UUID PRIMARY KEY DEFAULT uuid_generate_v4(),
+    name            TEXT NOT NULL,
+    spool_weight_g  INTEGER NOT NULL CHECK (spool_weight_g > 0),
+    is_system       BOOLEAN NOT NULL DEFAULT FALSE,
+    user_id         UUID REFERENCES users (id) ON DELETE CASCADE,
+    created_at      TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+
+    -- Presets do sistema não têm user_id; presets customizados têm
+    CONSTRAINT chk_preset_ownership CHECK (
+        (is_system = TRUE AND user_id IS NULL) OR
+        (is_system = FALSE AND user_id IS NOT NULL)
+    )
+);
+
+CREATE INDEX idx_spool_presets_user_id  ON spool_presets (user_id) WHERE user_id IS NOT NULL;
+CREATE INDEX idx_spool_presets_is_system ON spool_presets (is_system);
+
+-- Presets built-in do sistema (somente leitura para usuários)
+INSERT INTO spool_presets (name, spool_weight_g, is_system) VALUES
+    ('Bambu Lab (Plástico)',   250, TRUE),
+    ('Elegoo (Papelão)',       200, TRUE),
+    ('Creality (Plástico)',    230, TRUE),
+    ('Prusament (Plástico)',   201, TRUE),
+    ('Sunlu (Papelão)',        200, TRUE),
+    ('Polymaker (Plástico)',   220, TRUE),
+    ('Genérico Papelão 1kg',   200, TRUE),
+    ('Genérico Plástico 1kg',  250, TRUE);

backend/migrations/20240101000003_create_filaments.sql

@@ -0,0 +1,26 @@
+-- Migration: 003 - Criar tabela de filamentos
+
+CREATE TABLE filaments (
+    id               UUID PRIMARY KEY DEFAULT uuid_generate_v4(),
+    user_id          UUID NOT NULL REFERENCES users (id) ON DELETE CASCADE,
+    material         TEXT NOT NULL,
+    brand            TEXT NOT NULL,
+    model            TEXT,
+    color_hex        TEXT NOT NULL,
+    spool_preset_id  UUID NOT NULL REFERENCES spool_presets (id),
+    total_weight_g   INTEGER NOT NULL CHECK (total_weight_g > 0),
+    net_weight_g     INTEGER NOT NULL CHECK (net_weight_g >= 0),
+    temp_hotend_c    INTEGER CHECK (temp_hotend_c > 0),
+    temp_bed_c       INTEGER CHECK (temp_bed_c >= 0),
+    flow_factor_pct  DOUBLE PRECISION CHECK (flow_factor_pct > 0),
+    notes            TEXT,
+    updated_at       TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    created_at       TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+CREATE INDEX idx_filaments_user_id   ON filaments (user_id);
+CREATE INDEX idx_filaments_material  ON filaments (user_id, material);
+CREATE INDEX idx_filaments_brand     ON filaments (user_id, brand);
+CREATE INDEX idx_filaments_updated_at ON filaments (user_id, updated_at DESC);
+-- Índice para suporte a alertas de estoque baixo
+CREATE INDEX idx_filaments_net_weight ON filaments (user_id, net_weight_g);