feat: pass chat_template_kwargs through agent chat completion (#14542)

### What problem does this PR solve?

The agent API currently does not pass chat_template_kwargs to the
underlying LLM call path, so clients cannot control template-level model
behavior (such as thinking-mode toggles) when invoking
/agents/chat/completion. This PR adds passthrough support for
chat_template_kwargs across agent execution flows (session and
non-session, streaming and non-streaming) by propagating it through
canvas runtime state and into LLM invocation kwargs. This addresses the
feature gap raised in [Issue
#14182](https://github.com/infiniflow/ragflow/issues/14182).

Closes #14182 

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

test/unit_test/api/apps/sdk/test_dify_retrieval.py

@@ -1,4 +1,4 @@
-#
+#
 #  Copyright 2026 The InfiniFlow Authors. All Rights Reserved.
 #
 #  Licensed under the Apache License, Version 2.0 (the "License");