fix: Antigravity token refresh clientSecret and OpenCode Zen modelsUrl (#588, #612)

- Set clientSecretDefault for Antigravity provider (was empty, causing
  'client_secret is missing' on token refresh for npm users)
- Add modelsUrl to opencode-zen registry for 'Import from /models'

open-sse/config/providerRegistry.ts

@@ -386,7 +386,7 @@ export const REGISTRY: Record<string, RegistryEntry> = {
       clientIdEnv: "ANTIGRAVITY_OAUTH_CLIENT_ID",
       clientIdDefault: "1071006060591-tmhssin2h21lcre235vtolojh4g403ep.apps.googleusercontent.com",
       clientSecretEnv: "ANTIGRAVITY_OAUTH_CLIENT_SECRET",
-      clientSecretDefault: "",
+      clientSecretDefault: "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",
     },
     models: [
       { id: "claude-opus-4-6-thinking", name: "Claude Opus 4.6 Thinking" },
@@ -576,6 +576,7 @@ export const REGISTRY: Record<string, RegistryEntry> = {
     format: "openai",
     executor: "opencode",
     baseUrl: "https://opencode.ai/zen/v1",
+    modelsUrl: "https://opencode.ai/zen/v1/models",
     authType: "apikey",
     authHeader: "Authorization",
     authPrefix: "Bearer",