feat: silent wechat login, marketing tab optimization, admin page foundation

- Add silent WeChat login for MP/browser environments
- Fix Python 3.6 compatibility (remove typing.Annotated usage)
- Marketing page: tab-based content generation with category support
- Translate page: add auto-detect language default
- Homepage: add TTS playback, announcement ticker, remove redundant quick-actions
- Fix FAB button overlap with custom tabbar on customers/quotation pages
- Make openai/anthropic imports lazy for Python 3.6 compat

backend/app/ai/providers/openai.py

@@ -1,6 +1,5 @@
 from typing import Dict, Any, Optional
 import json
-from openai import AsyncOpenAI
 from app.ai.base import AIProvider
 
 
@@ -20,6 +19,13 @@ SYSTEM_PROMPTS = {
 
 class OpenAIProvider(AIProvider):
     def __init__(self, api_key: str, model: str = "gpt-4o", base_url: Optional[str] = None):
+        try:
+            from openai import AsyncOpenAI
+        except ImportError:
+            raise ImportError(
+                "openai>=1.0 is required for OpenAIProvider. "
+                "Install it with: pip install 'openai>=1.0'"
+            )
         kwargs = {"api_key": api_key}
         if base_url:
             kwargs["base_url"] = base_url