feat: AI assistant phase 2 - configurable prompt, action operations, FAQ matching, NVIDIA provider

- Admin-configurable AI prompt/quick questions from system_configs DB
- GET /api/v1/ai/quick-questions endpoint for fetching quick questions
- Local FAQ matching for instant responses (avoid AI calls for common Qs)
- AI action extraction: "add customer" intent detected, structured data returned
- Frontend action confirmation card with editable fields, calls customer API on confirm
- NVIDIA provider (stepfun-ai/step-3.5-flash) for faster chat vs deepseek-v4-flash
- Fixed httpx client timeout preventing backend hangs
- Added log_usage calls for auth events (register/login/guest/wechat)
- Admin tabs (users/stats/logs/config) fully functional with real backend
- AiAssistant component added to all tabbar pages

backend/app/ai/router.py

@@ -1,6 +1,6 @@
 from typing import Dict, Any, Optional, List
 from app.ai.base import AIProvider
-from app.ai.providers import OpenAIProvider, ClaudeProvider, DeepLProvider, LocalProvider, SparkProvider, SensenovaProvider, OpencodeGoProvider
+from app.ai.providers import OpenAIProvider, ClaudeProvider, DeepLProvider, LocalProvider, SparkProvider, SensenovaProvider, OpencodeGoProvider, NvidiaProvider
 from app.config import settings
 from app.ai.trade_corpus import TradeCorpus
 import logging
@@ -45,6 +45,17 @@ class AIRouter:
             except Exception as e:
                 logger.warning(f"OpencodeGo init failed: {e}")
 
+        if settings.NVIDIA_API_KEY:
+            try:
+                self.providers["nvidia"] = NvidiaProvider(
+                    api_key=settings.NVIDIA_API_KEY,
+                    model=settings.NVIDIA_MODEL,
+                    base_url=settings.NVIDIA_BASE_URL,
+                )
+                logger.info("Nvidia provider ready")
+            except Exception as e:
+                logger.warning(f"Nvidia init failed: {e}")
+
         if settings.ANTHROPIC_API_KEY:
             try:
                 self.providers["anthropic"] = ClaudeProvider(api_key=settings.ANTHROPIC_API_KEY)
@@ -132,6 +143,9 @@ class AIRouter:
     async def extract(self, text: str, schema: Dict[str, Any]) -> Dict[str, Any]:
         return await self.execute("extract", "extract_info", text, schema)
 
+    async def chat(self, message: str, history: list = None, system_prompt: str = None) -> Dict[str, Any]:
+        return await self.execute("chat", "chat", message, history, system_prompt)
+
 
 _router_instance = None