fix: simphtml visibility/dialog/SVG improvements & minor agent fixes

- simphtml: rewrite visibility inheritance (area-based maxC), add isVisible to childrenInfo,
  fix className SVG compat (getAttribute), expand isDialog detection, hoist deep fixed dialogs,
  clear SVG attrs, fix warning message concat
- ga: return error messages instead of None for code_run/web_execute_js failures
- stapp: disable unsafe_allow_html
- code_run_header: add excepthook hint for ImportError/AttributeError
- mykey_template: remove stale prompt_cache comment

mykey_template.py

@@ -20,7 +20,6 @@ oai_config = {
     'model': 'openai/gpt-5.1',
     'api_mode': 'chat_completions',  # 'chat_completions' | 'responses'
     # 'reasoning_effort': 'low',     # none|low|medium|high|xhigh (OpenAI o系列)
-    # 'prompt_cache': False,
     'max_retries': 2,                # 429/timeout/5xx 重试次数
     'connect_timeout': 10,           # 秒
     'read_timeout': 120,             # 秒（流式读取）