docs: 更新 AGENTS.md 添加热词功能说明

- 添加热词功能配置示例
- 说明实现原理和 API 细节
- 更新项目结构，添加 asr/hotwords.go

AGENTS.md

@@ -163,3 +163,36 @@ Per-connection loggers via `slog.With("remote", addr)`.
 - Config file (`config.yaml`) is gitignored; `config.example.yaml` is committed
 - `os.UserCacheDir()` for platform-correct cert cache paths
 - robotgo paste: `KeyDown(modifier)` → delay → `KeyTap("v")` → delay → `KeyUp(modifier)`
+
+## Hotwords (热词) Feature
+
+Local hotword management for improved ASR accuracy on specific terms (names, technical vocabulary).
+
+### Configuration
+
+```yaml
+doubao:
+  hotwords:
+    - 张三
+    - 李四
+    - VoicePaste
+    - 人工智能
+```
+
+### Implementation
+
+- Hotwords stored locally in `config.yaml` (not tied to cloud provider)
+- `BuildHotwordsContext()` converts string array to Doubao API format:
+  ```json
+  {"hotwords":[{"word":"张三"},{"word":"李四"}]}
+  ```
+- Sent via `corpus.context` parameter in `FullClientRequest`
+- Hot-reloadable: config changes apply to new connections
+- Platform-agnostic design: easy to migrate to other ASR providers
+
+### Doubao API Details
+
+- Parameter: `request.corpus.context` (JSON string)
+- Limits: 100 tokens (双向流式), 5000 tokens (流式输入)
+- Priority: `context` hotwords > `boosting_table_id` (if both present)
+- No weight support in `context` mode (unlike `boosting_table_id`)