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.

hermes_cli/main.py

@@ -2374,8 +2374,6 @@ def select_provider_and_model(args=None):
     # Step 2: Provider-specific setup + model selection
     if selected_provider == "openrouter":
         _model_flow_openrouter(config, current_model)
-    elif selected_provider == "ai-gateway":
-        _model_flow_ai_gateway(config, current_model)
     elif selected_provider == "nous":
         _model_flow_nous(config, current_model, args=args)
     elif selected_provider == "openai-codex":
@@ -2962,59 +2960,6 @@ def _model_flow_openrouter(config, current_model=""):
         print("No change.")
 
 
-def _model_flow_ai_gateway(config, current_model=""):
-    """Vercel AI Gateway provider: ensure API key, then pick model with pricing."""
-    from hermes_constants import AI_GATEWAY_BASE_URL
-    from hermes_cli.auth import (
-        PROVIDER_REGISTRY,
-        _prompt_model_selection,
-        _save_model_choice,
-        deactivate_provider,
-    )
-    from hermes_cli.config import get_env_value
-
-    # Route through _prompt_api_key so users can replace a stale/broken key
-    # in-flow (K/R/C) instead of having to edit ~/.hermes/.env by hand.
-    pconfig = PROVIDER_REGISTRY["ai-gateway"]
-    existing_key = get_env_value("AI_GATEWAY_API_KEY") or ""
-    if not existing_key:
-        print(
-            "Create API key here: https://vercel.com/d?to=%2F%5Bteam%5D%2F%7E%2Fai-gateway&title=AI+Gateway"
-        )
-        print("Add a payment method to get $5 in free credits.")
-        print()
-    _resolved, abort = _prompt_api_key(pconfig, existing_key, provider_id="ai-gateway")
-    if abort:
-        return
-
-    from hermes_cli.models import ai_gateway_model_ids, get_pricing_for_provider
-
-    models_list = ai_gateway_model_ids(force_refresh=True)
-    pricing = get_pricing_for_provider("ai-gateway", force_refresh=True)
-
-    selected = _prompt_model_selection(
-        models_list, current_model=current_model, pricing=pricing
-    )
-    if selected:
-        _save_model_choice(selected)
-
-        from hermes_cli.config import load_config, save_config
-
-        cfg = load_config()
-        model = cfg.get("model")
-        if not isinstance(model, dict):
-            model = {"default": model} if model else {}
-            cfg["model"] = model
-        model["provider"] = "ai-gateway"
-        model["base_url"] = AI_GATEWAY_BASE_URL
-        model["api_mode"] = "chat_completions"
-        save_config(cfg)
-        deactivate_provider()
-        print(f"Default model set to: {selected} (via Vercel AI Gateway)")
-    else:
-        print("No change.")
-
-
 def _model_flow_nous(config, current_model="", args=None):
     """Nous Portal provider: ensure logged in, then pick model."""
     from hermes_cli.auth import (