feat(cliproxy): add xAI Grok provider

config/base-xai.settings.json

@@ -0,0 +1,10 @@
+{
+  "env": {
+    "ANTHROPIC_BASE_URL": "http://127.0.0.1:8317/api/provider/xai",
+    "ANTHROPIC_AUTH_TOKEN": "ccs-internal-managed",
+    "ANTHROPIC_MODEL": "grok-build-0.1",
+    "ANTHROPIC_DEFAULT_OPUS_MODEL": "grok-4.5",
+    "ANTHROPIC_DEFAULT_SONNET_MODEL": "grok-build-0.1",
+    "ANTHROPIC_DEFAULT_HAIKU_MODEL": "grok-composer-2.5-fast"
+  }
+}