fix: address review feedback for Vercel AI Gateway PR

- Add --vercel-ai-gateway CLI option to install command
- Fix librarian/explore priority: native providers (ZAI, Copilot) now take precedence over Vercel gateway
- Add hasVercelAiGateway to installer no-provider warning conditions
- Add hasVercelAiGateway: false to all test file InstallConfig fixtures
- Fix test expectations for model ID format (claude-opus-4.6 vs claude-opus-4-6)

src/cli/model-fallback.ts

@@ -129,10 +129,10 @@ export function generateModelConfig(config: InstallConfig): GeneratedOmoConfig {
       let agentConfig: AgentConfig | undefined
       if (avail.opencodeGo) {
         agentConfig = { model: "opencode-go/minimax-m2.7" }
-      } else if (avail.vercelAiGateway) {
-        agentConfig = { model: "vercel/minimax/minimax-m2.7" }
       } else if (avail.zai) {
         agentConfig = { model: ZAI_MODEL }
+      } else if (avail.vercelAiGateway) {
+        agentConfig = { model: "vercel/minimax/minimax-m2.7" }
       }
       if (agentConfig) {
         agents[role] = attachAllFallbackModels(agentConfig, req.fallbackChain, avail)
@@ -148,10 +148,10 @@ export function generateModelConfig(config: InstallConfig): GeneratedOmoConfig {
         agentConfig = { model: "opencode/claude-haiku-4-5" }
       } else if (avail.opencodeGo) {
         agentConfig = { model: "opencode-go/minimax-m2.7" }
-      } else if (avail.vercelAiGateway) {
-        agentConfig = { model: "vercel/minimax/minimax-m2.7-highspeed" }
       } else if (avail.copilot) {
         agentConfig = { model: "github-copilot/gpt-5-mini" }
+      } else if (avail.vercelAiGateway) {
+        agentConfig = { model: "vercel/minimax/minimax-m2.7-highspeed" }
       } else {
         agentConfig = { model: "opencode/gpt-5-nano" }
       }