fix: address self-review findings for Vercel Sandbox salvage

- Add vercel_sandbox to hardline blocklist container bypass test
- Add vercel_sandbox to skills_tool remote backend parametrize test
- Deduplicate runtime set: doctor.py and setup.py now import
  _SUPPORTED_VERCEL_RUNTIMES from terminal_tool.py
- Add docstring to _run_bash explaining timeout/stdin_data discards
- Always stop sandbox during cleanup (unconditional, matching Modal/Daytona)
- Update security.md: container bypass text, production tip, comparison table
- Update environment-variables.md: TERMINAL_ENV list, Vercel auth vars,
  TERMINAL_VERCEL_RUNTIME
- Update inline comments in cli.py and config.py to include vercel_sandbox

hermes_cli/web_server.py

@@ -258,7 +258,7 @@ _SCHEMA_OVERRIDES: Dict[str, Dict[str, Any]] = {
     "terminal.vercel_runtime": {
         "type": "select",
         "description": "Vercel Sandbox runtime",
-        "options": ["node24", "node22", "python3.13"],
+        "options": ["node24", "node22", "python3.13"],  # sync with _SUPPORTED_VERCEL_RUNTIMES in terminal_tool.py
     },
     "terminal.modal_mode": {
         "type": "select",