docs: sync code blocks and generate API reference (#192)

Synced from agent-sdk ref: main

Co-authored-by: xingyaoww <38853559+xingyaoww@users.noreply.github.com>

Author: github-actions[bot]

sdk/api-reference/openhands.sdk.llm.mdx

@@ -617,6 +617,7 @@ Bases: `BaseContent`
 #### Properties
 
 - `cache_prompt`: bool
+- `enable_truncation`: bool
 - `model_config`: ClassVar[ConfigDict] = (configuration object)
   Configuration for the model, should be a dictionary conforming to [ConfigDict][pydantic.config.ConfigDict].
 - `text`: str
@@ -643,6 +644,6 @@ and passed back to the API for tool use scenarios.
 
 - `model_config`: ClassVar[ConfigDict] = (configuration object)
   Configuration for the model, should be a dictionary conforming to [ConfigDict][pydantic.config.ConfigDict].
-- `signature`: str
+- `signature`: str | None
 - `thinking`: str
 - `type`: Literal['thinking']