feat: add Chinese UI, Responses models, and mirrored Windows setup

Localize the web console and persist custom model and capability settings.
Use OpenAI Responses exclusively and move runtime limits into environment configuration.
Bootstrap uv and the virtual environment on Windows, support optional China mirrors,
and package source distributions without environments, build output, or credentials.

Update regression tests and repository quality checks for the new behavior.

artemis/agents/explorer/universal_runner.py

@@ -30,6 +30,8 @@ from langchain_core.messages import (
     ToolMessage,
 )
 
+from artemis.llm.structured import content_to_text
+
 from artemis.agents.explorer.geometry import is_valid_norm_point
 from artemis.agents.explorer.tiers import SUBMIT_TOOL
 from artemis.agents.explorer.tool_declarations import UNIVERSAL_EXPLORER_TOOLS
@@ -128,7 +130,8 @@ class UniversalRunnerMixin:
                     return json.dumps(
                         {
                             "candidates": [],
-                            "fallback_message": str(response.content) or "No candidates found.",
+                            "fallback_message": content_to_text(response.content)
+                            or "No candidates found.",
                         },
                         ensure_ascii=False,
                     )