feat: add GitHub Copilot provider

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

src/cli/models-cli.ts

@@ -1,6 +1,7 @@
 import type { Command } from "commander";
 
 import {
+  githubCopilotLoginCommand,
   modelsAliasesAddCommand,
   modelsAliasesListCommand,
   modelsAliasesRemoveCommand,
@@ -374,6 +375,31 @@ export function registerModelsCli(program: Command) {
       }
     });
 
+  auth
+    .command("login-github-copilot")
+    .description(
+      "Login to GitHub Copilot via GitHub device flow (TTY required)",
+    )
+    .option(
+      "--profile-id <id>",
+      "Auth profile id (default: github-copilot:github)",
+    )
+    .option("--yes", "Overwrite existing profile without prompting", false)
+    .action(async (opts) => {
+      try {
+        await githubCopilotLoginCommand(
+          {
+            profileId: opts.profileId as string | undefined,
+            yes: Boolean(opts.yes),
+          },
+          defaultRuntime,
+        );
+      } catch (err) {
+        defaultRuntime.error(String(err));
+        defaultRuntime.exit(1);
+      }
+    });
+
   const order = auth
     .command("order")
     .description("Manage per-agent auth profile order overrides");