fix(deps): fix lint errors from langchain/langfuse upgrade

- common/llm.py: Remove secret_key and host args from langfuse 3.x
  CallbackHandler (reads from env vars automatically via get_client)
- seed-gen/task.py: Fix import sort order after langchain_core.prompts move

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

common/src/buttercup/common/llm.py

@@ -81,11 +81,9 @@ def get_langfuse_callbacks() -> list[BaseCallbackHandler]:
         try:
             from langfuse.langchain import CallbackHandler
 
-            langfuse_handler = CallbackHandler(
-                public_key=os.getenv("LANGFUSE_PUBLIC_KEY"),
-                secret_key=os.getenv("LANGFUSE_SECRET_KEY"),
-                host=os.getenv("LANGFUSE_HOST"),
-            )
+            # langfuse 3.x reads LANGFUSE_PUBLIC_KEY, LANGFUSE_SECRET_KEY,
+            # and LANGFUSE_HOST from env vars automatically via get_client()
+            langfuse_handler = CallbackHandler()
             if langfuse_auth_check():
                 logger.info("Tracing with LangFuse enabled")
                 return [langfuse_handler]

seed-gen/src/buttercup/seed_gen/task.py

@@ -12,9 +12,9 @@ from buttercup.common.llm import ButtercupLLM, create_default_llm, get_langfuse_
 from buttercup.common.project_yaml import ProjectYaml
 from buttercup.program_model.codequery import CodeQueryPersistent
 from buttercup.program_model.utils.common import Function, TypeDefinition
-from langchain_core.prompts import ChatPromptTemplate
 from langchain_core.language_models import BaseChatModel
 from langchain_core.messages import BaseMessage, ToolMessage
+from langchain_core.prompts import ChatPromptTemplate
 from langchain_core.tools import BaseTool, tool
 from langchain_core.tools.base import InjectedToolCallId
 from langgraph.graph import add_messages