Prevent historical assistant reasoning_content from being replayed to
generic/local providers by default while preserving current behavior for
known reasoning-capable provider protocols.
Adds a webui.reasoning_content_replay policy read by the sanitizer:
auto, strip, and preserve. Auto strips for local/generic backends such as
LM Studio/Ollama/llama.cpp and preserves for explicitly known provider
protocols that may require reasoning replay.
This only affects provider-facing sanitized history. It does not modify
stored session/display reasoning metadata.
