feat: add GitHub Copilot provider

Copilot device login + onboarding option; model list auth detection.

src/cli/models-cli.test.ts

@@ -0,0 +1,48 @@
+import { describe, expect, it, vi } from "vitest";
+
+const githubCopilotLoginCommand = vi.fn();
+
+vi.mock("../commands/models.js", async () => {
+  const actual = (await vi.importActual<typeof import("../commands/models.js")>(
+    "../commands/models.js",
+  )) as typeof import("../commands/models.js");
+
+  return {
+    ...actual,
+    githubCopilotLoginCommand,
+  };
+});
+
+describe("models cli", () => {
+  it("registers github-copilot login command", async () => {
+    const { Command } = await import("commander");
+    const { registerModelsCli } = await import("./models-cli.js");
+
+    const program = new Command();
+    registerModelsCli(program);
+
+    const models = program.commands.find((cmd) => cmd.name() === "models");
+    expect(models).toBeTruthy();
+
+    const auth = models?.commands.find((cmd) => cmd.name() === "auth");
+    expect(auth).toBeTruthy();
+
+    const login = auth?.commands.find(
+      (cmd) => cmd.name() === "login-github-copilot",
+    );
+    expect(login).toBeTruthy();
+
+    await program.parseAsync(
+      ["models", "auth", "login-github-copilot", "--yes"],
+      {
+        from: "user",
+      },
+    );
+
+    expect(githubCopilotLoginCommand).toHaveBeenCalledTimes(1);
+    expect(githubCopilotLoginCommand).toHaveBeenCalledWith(
+      expect.objectContaining({ yes: true }),
+      expect.any(Object),
+    );
+  });
+});