docs: 修复文档中过时的字段、签名和缺失的类

- BaseConfig 的 from_json/to_json → from_file/to_file
- InputConfig/ProcessingConfig/OutputConfig 字段对齐源码
- 移除不存在的 Registry 类，register() 去 category/priority
- SchedulerFactory.create 参数顺序修正
- 架构图/训练/参数文档补全 WSDScheduler
- CONTRIBUTING.md 克隆地址占位符修正
- params.md label_smoothing 默认值修正，补全 neftune_alpha
- app 类更正为 get_app 函数

assets/docs/training.md

@@ -127,8 +127,9 @@ Keys: `prompts`, `responses`, `masks`, `rewards`.
 |------|-------|-------------|
 | Cosine | `CosineScheduler` | Linear warmup → cosine decay to `min_rate` |
 | SGDR | `SGDRScheduler` | Cosine annealing with warm restarts (`t_mult=2`) |
+| WSD | `WSDScheduler` | Warmup-Stable-Decay with sqrt cooldown |
 
-Created by `SchedulerFactory.create(optimizer, schedule_type, **kwargs)`. Valid types: `"cosine"`, `"sgdr"`. Omit to use no scheduler.
+Created by `SchedulerFactory.create(schedule_type, optimizer, **kwargs)`. Valid types: `"cosine"`, `"sgdr"`, `"wsd"`. Omit to use no scheduler.
 
 ## Gradient Checkpointing