feat(db): add pricing config fields to proxy_config table

- Add default_cost_multiplier field per app type
- Add pricing_model_source field (request/response)
- Add request_model field to proxy_request_logs table
- Implement schema migration v5

src-tauri/src/database/mod.rs

@@ -47,7 +47,7 @@ const DB_BACKUP_RETAIN: usize = 10;
 
 /// 当前 Schema 版本号
 /// 每次修改表结构时递增，并在 schema.rs 中添加相应的迁移逻辑
-pub(crate) const SCHEMA_VERSION: i32 = 4;
+pub(crate) const SCHEMA_VERSION: i32 = 5;
 
 /// 安全地序列化 JSON，避免 unwrap panic
 pub(crate) fn to_json_string<T: Serialize>(value: &T) -> Result<String, AppError> {