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

assets/code_run_header.py

@@ -19,4 +19,4 @@ def _run(*a, **k):
         if r.stderr is not None: r.stderr = _d(r.stderr)
     return r
 subprocess.run = _run
-
+sys.excepthook = lambda t, v, tb: (sys.__excepthook__(t, v, tb), print(f"\n[Agent Hint]: NO GUESSING! You MUST probe first. If missing common package, pip.")) if issubclass(t, (ImportError, AttributeError)) else sys.__excepthook__(t, v, tb)