* fix: migrate from deprecated create_react_agent to langchain.agents.create_agent
Fixes#799
- Replace deprecated langgraph.prebuilt.create_react_agent with
langchain.agents.create_agent (LangGraph 1.0 migration)
- Add DynamicPromptMiddleware to handle dynamic prompt templates
(replaces the 'prompt' callable parameter)
- Add PreModelHookMiddleware to handle pre-model hooks
(replaces the 'pre_model_hook' parameter)
- Update AgentState import from langchain.agents in template.py
- Update tests to use the new API
* fix:update the code with review comments
* feat: Add comprehensive Chinese localization support for issue #412
- Add locale parameter to ChatRequest model to capture user's language preference
- Implement language-aware template loading in template.py with fallback to English
- Update all apply_prompt_template calls to pass locale through the workflow
- Create Chinese translations for 14 core prompt files:
* Main agents: coordinator, planner, researcher, reporter, coder
* Subprocess agents: podcast_script_writer, ppt_composer, prompt_enhancer
* Writing assistant: all 6 prose prompts
- Update app.py to extract and propagate locale through workflow state
- Support both zh-CN and en-US locales with automatic fallback
- Ensure locale flows through all agent nodes and template rendering
* address the review suggestions