feat: 新增 MySQL 数据库驱动支持，支持跨设备数据同步

backend/migrations/sqlite/20260421000001_initial_schema.sql

@@ -0,0 +1,45 @@
+-- +goose Up
+-- 统一初始迁移：providers、models、usage_stats 完整表结构
+-- models 表使用 UUID 主键 + UNIQUE(provider_id, model_name) 联合唯一约束
+
+CREATE TABLE IF NOT EXISTS providers (
+    id TEXT PRIMARY KEY,
+    name TEXT NOT NULL,
+    api_key TEXT NOT NULL,
+    base_url TEXT NOT NULL,
+    protocol TEXT DEFAULT 'openai',
+    enabled INTEGER DEFAULT 1,
+    created_at DATETIME,
+    updated_at DATETIME
+);
+
+CREATE TABLE IF NOT EXISTS models (
+    id TEXT PRIMARY KEY,
+    provider_id TEXT NOT NULL,
+    model_name TEXT NOT NULL,
+    enabled INTEGER DEFAULT 1,
+    created_at DATETIME,
+    FOREIGN KEY (provider_id) REFERENCES providers(id) ON DELETE CASCADE,
+    UNIQUE(provider_id, model_name)
+);
+
+CREATE TABLE IF NOT EXISTS usage_stats (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    provider_id TEXT NOT NULL,
+    model_name TEXT NOT NULL,
+    request_count INTEGER DEFAULT 0,
+    date DATE NOT NULL,
+    UNIQUE(provider_id, model_name, date)
+);
+
+CREATE INDEX IF NOT EXISTS idx_models_provider_id ON models(provider_id);
+CREATE INDEX IF NOT EXISTS idx_models_model_name ON models(model_name);
+CREATE INDEX IF NOT EXISTS idx_usage_stats_provider_model_date ON usage_stats(provider_id, model_name, date);
+
+-- +goose Down
+DROP INDEX IF EXISTS idx_usage_stats_provider_model_date;
+DROP INDEX IF EXISTS idx_models_model_name;
+DROP INDEX IF EXISTS idx_models_provider_id;
+DROP TABLE IF EXISTS usage_stats;
+DROP TABLE IF EXISTS models;
+DROP TABLE IF EXISTS providers;