mcp-config: add covert-gpt provider, auto-discover models

Two changes to the synced opencode config:

- Model provider. opencode can't list models from a custom OpenAI-compatible
  provider itself, so sync.sh queries the gateway's /v1/models with the
  user's key and materializes the map client-side. New gateway models land
  on every box at the next sync with no config edit. If discovery fails the
  previous map is carried over, so a gateway hiccup never empties the list.
- Aggregate MCP endpoint. One entry at /mcp/ (trailing slash required — the
  bare path 307-redirects and MCP clients don't follow it) exposes every
  server the key can access, replacing the per-server gitea entry.

sync.sh also exports OPENCODE_CONFIG: opencode does not auto-load extra
files from its config dir, so without it the synced file was ignored.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

mcp-config/opencode.gateway.json

@@ -1,9 +1,20 @@
 {
   "$schema": "https://opencode.ai/config.json",
+  "provider": {
+    "covert-gpt": {
+      "npm": "@ai-sdk/openai-compatible",
+      "name": "covert-gpt (LiteLLM)",
+      "options": {
+        "baseURL": "https://llm.covert-gpt.com/v1",
+        "apiKey": "{env:LITELLM_KEY}"
+      },
+      "models": {}
+    }
+  },
   "mcp": {
-    "gitea": {
+    "covert-gpt": {
       "type": "remote",
-      "url": "https://llm.covert-gpt.com/mcp/gitea",
+      "url": "https://llm.covert-gpt.com/mcp/",
       "enabled": true,
       "headers": {
         "Authorization": "Bearer {env:LITELLM_KEY}"