feat: add OpenCode Go provider and support for custom models

- Introduced OpenCode Go provider with relevant configurations.
- Enhanced model management by allowing users to add and delete custom models.
- Updated UI components to support model selection for image types.
- Adjusted sidebar visibility to include image media kinds.

open-sse/config/providers.js

@@ -337,6 +337,11 @@ export const PROVIDERS = {
     headers: { "x-opencode-client": "desktop" },
     noAuth: true
   },
+  "opencode-go": {
+    baseUrl: "https://opencode.ai/zen/go/v1/chat/completions",
+    format: "openai",
+    headers: {}
+  },
   "grok-web": {
     baseUrl: "https://grok.com/rest/app-chat/conversations/new",
     format: "grok-web",