remove Vercel AI Gateway and Vercel Sandbox (#33067)

* remove Vercel AI Gateway provider and Vercel Sandbox terminal backend

Both Vercel-hosted integrations are removed end-to-end. Users on the AI
Gateway should switch to OpenRouter or one of the other aggregators
(Nous Portal, Kilo Code). Users on the Vercel Sandbox backend should
switch to Docker, Modal, Daytona, or SSH.

What's removed:
- `plugins/model-providers/ai-gateway/` provider plugin
- `hermes_cli/vercel_auth.py` Vercel-Sandbox auth helper
- `tools/environments/vercel_sandbox.py` terminal backend
- `ai-gateway` provider wiring across auth, doctor, setup, models,
  config, status, providers, main, web_server, model_normalize, dump
- `vercel_sandbox` backend wiring across terminal_tool, file_tools,
  code_execution_tool, file_operations, approval, skills_tool,
  environments/local, credential_files, lazy_deps, prompt_builder,
  cli, gateway/run
- `AI_GATEWAY_BASE_URL` constant, `_AI_GATEWAY_HEADERS` auxiliary-client
  header set, run_agent base-URL header/reasoning special-cases
- `[vercel]` pyproject extra and `vercel`/`vercel-workers` from uv.lock
- env vars: `AI_GATEWAY_API_KEY`, `AI_GATEWAY_BASE_URL`, `VERCEL_TOKEN`,
  `VERCEL_PROJECT_ID`, `VERCEL_TEAM_ID`, `VERCEL_OIDC_TOKEN`,
  `TERMINAL_VERCEL_RUNTIME`
- Tests: deletes test_ai_gateway_models.py and
  test_vercel_sandbox_environment.py; scrubs references across 23
  surviving test files (no entire tests deleted unless they were
  dedicated to AI Gateway / Sandbox)
- Docs: provider tables, env-var reference, setup guides, security
  notes, tool config, terminal-backend tables — English plus zh-Hans
  i18n parity
- `hermes-agent` skill: provider table entry and remote-backend list

What stays (intentional):
- `popular-web-designs/templates/vercel.md` — CSS design reference,
  unrelated to Vercel-the-AI-product
- `x-vercel-id` in `stream_diag.py` headers — generic Vercel CDN
  response header, useful diag signal on any Vercel-hosted endpoint
- `vercel-labs/agent-browser` URL in browser config — lightpanda
  browser project, different OSS effort
- `userStories.json` historical contributor entry mentioning Vercel
  Sandbox — archive, not active docs

Validation:
- 1153 tests in the 22 targeted files pass (`scripts/run_tests.sh`)
- Full repo `py_compile` clean
- Live import of every touched module + invariant check (no
  `ai-gateway` in `PROVIDER_REGISTRY`, no `_AI_GATEWAY_HEADERS`, no
  `vercel_sandbox` in `_REMOTE_TERMINAL_BACKENDS`)

* test: convert profile-count check from change-detector to invariant

The hardcoded "== 34" assertion broke when ai-gateway was removed.
Per AGENTS.md change-detector-test guidance, assert the relationship
(registry count >= number of plugin dirs) instead of a literal count.
Counts shift when providers are added/removed; that's expected.

website/i18n/zh-Hans/docusaurus-plugin-content-docs/current/user-guide/security.md

@@ -144,7 +144,7 @@ approvals:
 | `gateway run` 配合 `&`/`disown`/`nohup`/`setsid` | 防止在服务管理器外启动 gateway |
 
 :::info
-**容器绕过**：在 `docker`、`singularity`、`modal`、`daytona` 或 `vercel_sandbox` 后端运行时，危险命令检查会被**跳过**，因为容器本身就是安全边界。容器内的破坏性命令不会危害宿主机。
+**容器绕过**：在 `docker`、`singularity`、`modal` 或 `daytona` 后端运行时，危险命令检查会被**跳过**，因为容器本身就是安全边界。容器内的破坏性命令不会危害宿主机。
 :::
 
 ### 审批流程（CLI）
@@ -340,7 +340,7 @@ terminal:
 - **临时模式**（`container_persistent: false`）：工作区使用 tmpfs——清理后所有内容丢失
 
 :::tip
-对于生产 gateway 部署，使用 `docker`、`modal`、`daytona` 或 `vercel_sandbox` 后端，将 Agent 命令与宿主机系统隔离。这样可以完全消除危险命令审批的需要。
+对于生产 gateway 部署，使用 `docker`、`modal` 或 `daytona` 后端，将 Agent 命令与宿主机系统隔离。这样可以完全消除危险命令审批的需要。
 :::
 
 :::warning
@@ -357,7 +357,6 @@ terminal:
 | **singularity** | 容器 | ❌ 跳过 | HPC 环境 |
 | **modal** | 云沙箱 | ❌ 跳过 | 可扩展的云隔离 |
 | **daytona** | 云沙箱 | ❌ 跳过 | 持久化云工作区 |
-| **vercel_sandbox** | 云微虚拟机 | ❌ 跳过 | 带快照持久化的云执行 |
 
 ## 环境变量透传 {#environment-variable-passthrough}