Rename OSS_PROXY_MODEL to DEFAULT_PROXY_MODEL; default Router proxy to Kimi K2.6.

Derive the platform default from moonshotai/kimi-k2 openRouterResolve, add models.dev drift coverage, and promote repos on default-branch workflow pushes when still needs_setup.

models.test.ts

@@ -1,5 +1,6 @@
 import { describe, expect, it } from "vitest";
 import {
+  DEFAULT_PROXY_MODEL,
   getModelEnvVars,
   getModelProvider,
   isBedrockAnthropicId,
@@ -134,6 +135,12 @@ describe("resolveDisplayAlias", () => {
   });
 });
 
+describe("DEFAULT_PROXY_MODEL", () => {
+  it("tracks moonshotai/kimi-k2 openRouterResolve", () => {
+    expect(DEFAULT_PROXY_MODEL).toBe(resolveOpenRouterModel("moonshotai/kimi-k2"));
+  });
+});
+
 describe("resolveOpenRouterModel", () => {
   it("returns the openrouter specifier for a non-deprecated alias", () => {
     expect(resolveOpenRouterModel("anthropic/claude-opus")).toBe(