feat: reject empty-string tokens in GenerateRequest (min_length=1)

backend/app/schemas.py

@@ -1,6 +1,6 @@
 from datetime import datetime
 from typing import Optional
-from pydantic import BaseModel
+from pydantic import BaseModel, Field
 
 
 # --- Auth ---
@@ -295,7 +295,7 @@ class ParamOut(BaseModel):
 
 # --- Generate ---
 class GenerateRequest(BaseModel):
-    token: Optional[str] = None
+    token: Optional[str] = Field(default=None, min_length=1)
 
 
 class RegenerateTokenOut(BaseModel):