feat(payment): Stripe Checkout payment module

- payment_orders 建表迁移，支持多 provider（stripe）
- Stripe Checkout Session 创建、Webhook 验签、到账
- 支付成功自动为 API Key 增加额度
- payment.enabled 开关，关闭时不影响旧 Comfy Checkout

src/config.rs

@@ -13,6 +13,8 @@ pub struct AppConfig {
     pub proxy: ProxyConfig,
     #[serde(default)]
     pub comfyui: ComfyUIConfig,
+    #[serde(default)]
+    pub payment: PaymentConfig,
 }
 
 #[derive(Debug, Deserialize, Clone)]
@@ -75,6 +77,23 @@ pub struct ComfyUIConfig {
     pub agent_model: String,
 }
 
+#[derive(Debug, Deserialize, Clone)]
+pub struct PaymentConfig {
+    pub enabled: bool,
+    pub public_base_url: Option<String>,
+    pub product_name_prefix: String,
+    pub currency: String,
+    pub min_amount_usd: f64,
+    pub max_amount_usd: Option<f64>,
+    pub daily_limit_usd: Option<f64>,
+    pub order_timeout_minutes: i64,
+    pub max_pending_orders: i64,
+    pub stripe_secret_key: Option<String>,
+    pub stripe_webhook_secret: Option<String>,
+    pub success_path: String,
+    pub cancel_path: String,
+}
+
 #[derive(Debug, Deserialize, Clone, Default)]
 #[serde(rename_all = "snake_case")]
 pub enum ComfyUIBackend {
@@ -116,6 +135,26 @@ impl Default for ComfyUIConfig {
     }
 }
 
+impl Default for PaymentConfig {
+    fn default() -> Self {
+        Self {
+            enabled: false,
+            public_base_url: None,
+            product_name_prefix: "BossAI 账户充值".to_string(),
+            currency: "usd".to_string(),
+            min_amount_usd: 1.0,
+            max_amount_usd: Some(100_000.0),
+            daily_limit_usd: None,
+            order_timeout_minutes: 30,
+            max_pending_orders: 3,
+            stripe_secret_key: None,
+            stripe_webhook_secret: None,
+            success_path: "/user/recharge?payment=success&order={ORDER_ID}".to_string(),
+            cancel_path: "/user/recharge?payment=cancel&order={ORDER_ID}".to_string(),
+        }
+    }
+}
+
 impl ComfyUIConfig {
     pub fn uses_native_backend(&self) -> bool {
         matches!(