refactor(ai): replace OpenAI with DeepSeek API

- Update config.py with DEEPSEEK_API_KEY, DEEPSEEK_MODEL, DEEPSEEK_BASE_URL
- Update ai.py to use DeepSeek endpoint (OpenAI-compatible)
- Update docker-compose.yml environment variables

services/flow-engine/app/config.py

@@ -6,9 +6,10 @@ class Settings(BaseSettings):
     DATABASE_URL: str = "postgresql://whatsapp_admin:password@localhost:5432/whatsapp_central"
     REDIS_URL: str = "redis://localhost:6379"
 
-    # OpenAI
-    OPENAI_API_KEY: str = ""
-    OPENAI_MODEL: str = "gpt-3.5-turbo"
+    # DeepSeek AI (OpenAI-compatible API)
+    DEEPSEEK_API_KEY: str = ""
+    DEEPSEEK_MODEL: str = "deepseek-chat"
+    DEEPSEEK_BASE_URL: str = "https://api.deepseek.com"
 
     API_GATEWAY_URL: str = "http://localhost:8000"
     WHATSAPP_CORE_URL: str = "http://localhost:3001"

services/flow-engine/app/nodes/ai.py

@@ -10,7 +10,7 @@ settings = get_settings()
 
 
 class AIResponseExecutor(NodeExecutor):
-    """Generate AI response using OpenAI"""
+    """Generate AI response using DeepSeek API"""
 
     async def execute(
         self, config: dict, context: FlowContext, session: Any
@@ -21,8 +21,8 @@ class AIResponseExecutor(NodeExecutor):
         max_tokens = config.get("max_tokens", 500)
         temperature = config.get("temperature", 0.7)
 
-        if not settings.OPENAI_API_KEY:
-            context.set("_ai_error", "OpenAI API key not configured")
+        if not settings.DEEPSEEK_API_KEY:
+            context.set("_ai_error", "DeepSeek API key not configured")
             return "error"
 
         if not prompt:
@@ -43,13 +43,13 @@ class AIResponseExecutor(NodeExecutor):
 
         async with httpx.AsyncClient() as client:
             response = await client.post(
-                "https://api.openai.com/v1/chat/completions",
+                f"{settings.DEEPSEEK_BASE_URL}/v1/chat/completions",
                 headers={
-                    "Authorization": f"Bearer {settings.OPENAI_API_KEY}",
+                    "Authorization": f"Bearer {settings.DEEPSEEK_API_KEY}",
                     "Content-Type": "application/json",
                 },
                 json={
-                    "model": settings.OPENAI_MODEL,
+                    "model": settings.DEEPSEEK_MODEL,
                     "messages": messages,
                     "max_tokens": max_tokens,
                     "temperature": temperature,
@@ -68,7 +68,7 @@ class AIResponseExecutor(NodeExecutor):
 
 
 class AISentimentExecutor(NodeExecutor):
-    """Analyze sentiment of user message"""
+    """Analyze sentiment of user message using DeepSeek"""
 
     async def execute(
         self, config: dict, context: FlowContext, session: Any
@@ -78,18 +78,18 @@ class AISentimentExecutor(NodeExecutor):
         )
         output_variable = config.get("output_variable", "_sentiment")
 
-        if not settings.OPENAI_API_KEY or not text:
+        if not settings.DEEPSEEK_API_KEY or not text:
             return "neutral"
 
         async with httpx.AsyncClient() as client:
             response = await client.post(
-                "https://api.openai.com/v1/chat/completions",
+                f"{settings.DEEPSEEK_BASE_URL}/v1/chat/completions",
                 headers={
-                    "Authorization": f"Bearer {settings.OPENAI_API_KEY}",
+                    "Authorization": f"Bearer {settings.DEEPSEEK_API_KEY}",
                     "Content-Type": "application/json",
                 },
                 json={
-                    "model": "gpt-3.5-turbo",
+                    "model": settings.DEEPSEEK_MODEL,
                     "messages": [
                         {
                             "role": "system",