fix(model-fallback): align OpenAI fallback resolution across CLI and runtime

Keep install-time and runtime model tables in sync, stop OpenAI-only misrouting when OpenCode Go is present, and add valid OpenAI fallbacks for atlas, metis, and sisyphus-junior.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/cli/openai-only-model-catalog.test.ts

@@ -13,6 +13,7 @@ function createConfig(overrides: Partial<InstallConfig> = {}): InstallConfig {
     hasOpencodeZen: false,
     hasZaiCodingPlan: false,
     hasKimiForCoding: false,
+    hasOpencodeGo: false,
     ...overrides,
   }
 }
@@ -43,4 +44,17 @@ describe("generateModelConfig OpenAI-only model catalog", () => {
     expect(result.categories?.["visual-engineering"]).toEqual({ model: "openai/gpt-5.4", variant: "high" })
     expect(result.categories?.writing).toEqual({ model: "openai/gpt-5.4", variant: "medium" })
   })
+
+  test("does not apply OpenAI-only overrides when OpenCode Go is also available", () => {
+    // #given
+    const config = createConfig({ hasOpenAI: true, hasOpencodeGo: true })
+
+    // #when
+    const result = generateModelConfig(config)
+
+    // #then
+    expect(result.agents?.explore).toEqual({ model: "opencode-go/minimax-m2.5" })
+    expect(result.agents?.librarian).toEqual({ model: "opencode-go/minimax-m2.5" })
+    expect(result.categories?.quick).toEqual({ model: "opencode-go/minimax-m2.5" })
+  })
 })