fix(grok): make the opencode runtime actually load — proven live on grok-build-0.1

Live verification (opencode 1.17.8 + grok-build-0.1, funded key) showed the Grok
runtime was loading INERT, three ways:

1. The provider override `provider.xai.npm=@ai-sdk/openai` failed model
   resolution (ProviderModelNotFoundError) — opencode can't resolve that package
   from its module path. Worse, ANY custom `provider.xai` block (even just
   options) breaks plugin-tool registration. opencode's BUILT-IN xai provider
   drives grok-build-0.1 with working tool-calls, so emit NO provider block; the
   key + base reach it via XAI_API_KEY / XAI_BASE_URL env (provider.options.apiKey
   alone does NOT authenticate).
2. Plugins referenced by absolute path in the config `plugin:` array never
   registered their hooks/tools. opencode 1.17.8 only registers from the plugin
   AUTO-DISCOVERY dir (~/.config/opencode/plugin/). Bake all plugins there.
3. Plugins must use a NAMED export, not `export default`.

Changes:
- opencode_config: no `provider` block, no `plugin` array; drop the dead
  XaiTarget + timeout machinery; build_opencode_config now takes a model string.
- GrokProvider / orchestrator interactive env: inject XAI_API_KEY + XAI_BASE_URL
  (drop the now-unused OPENAI_*).
- secret-scrub / budget-feed / secretary-tools / intake-tools: named exports;
  baked into /home/agent/.config/opencode/plugin/ (drop the EXTRA_PLUGINS env).
- agent-grok* Dockerfiles: plugin dir + agent ownership; drop the unneeded
  @ai-sdk/openai global install.

Verified live end-to-end: grok-build-0.1 calls read_company_state AND
submit_directive through secretary-tools.js and the backend receives both with
the agent token; a tool.execute.before guard fires; built-in tool-calls work.
Targeted gate green (ruff/mypy/xenon + opencode_config/providers/interactive
tests; node --check the plugins).

tests/unit/llm/test_providers.py

@@ -5,7 +5,7 @@ GrokProvider (xAI / OpenAI protocol) — especially the safety properties an
 OpenAI-protocol agent provider must hold:
 
   * the agent gets the MCP gateway wiring (reuses the orchestrator mount path);
-  * the xAI endpoint is injected as OPENAI_* and never mislabelled ANTHROPIC_*;
+  * the xAI endpoint is injected as XAI_* and never mislabelled ANTHROPIC_*;
   * the prompt travels via env, so a leading ``--`` cannot become a CLI flag.
 """
 
@@ -177,7 +177,7 @@ async def test_grok_spawn_requires_mcp_config() -> None:
         await provider.spawn(_config(mcp_config_path=None))
 
 
-async def test_grok_spawn_injects_openai_env_and_no_anthropic_leak() -> None:
+async def test_grok_spawn_injects_xai_env_and_no_anthropic_leak() -> None:
     host = _FakeHost()
     provider = GrokProvider(host, image="roboco-agent-grok:test")
     with patch(
@@ -185,8 +185,10 @@ async def test_grok_spawn_injects_openai_env_and_no_anthropic_leak() -> None:
     ) as exec_mock:
         await provider.spawn(_config(), initial_prompt="do the work")
     cmd = list(exec_mock.call_args.args)
-    assert "OPENAI_BASE_URL=https://api.x.ai/v1" in cmd
-    assert "OPENAI_API_KEY=xai-secret-key" in cmd
+    # opencode's built-in xai provider reads XAI_API_KEY / XAI_BASE_URL (no
+    # provider block in the rendered config — that breaks plugin-tool reg).
+    assert "XAI_API_KEY=xai-secret-key" in cmd
+    assert "XAI_BASE_URL=https://api.x.ai/v1" in cmd
     # The xAI endpoint must NOT be injected as an Anthropic var.
     assert not any(c.startswith("ANTHROPIC_BASE_URL=") for c in cmd)
     assert not any(c.startswith("ANTHROPIC_AUTH_TOKEN=") for c in cmd)
@@ -245,7 +247,7 @@ async def test_grok_spawn_defaults_base_url_when_route_blank() -> None:
     ) as exec_mock:
         await provider.spawn(_config(provider_base_url=None))
     cmd = list(exec_mock.call_args.args)
-    assert "OPENAI_BASE_URL=https://api.x.ai/v1" in cmd
+    assert "XAI_BASE_URL=https://api.x.ai/v1" in cmd
 
 
 async def test_grok_spawn_raises_on_docker_failure() -> None: