fix: use reasoning_content for Open WebUI streaming

Use DeepSeek R1 format (reasoning_content field) instead of <think>
tags in content. Open WebUI now renders thinking as proper
collapsible blocks instead of broken escaped HTML.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "tatlock"
-version = "1.8.2"
+version = "1.8.3"
 description = "OpenAI-compatible API with Ollama backend"
 requires-python = ">=3.12"
 dependencies = []