core: bundle GitLab auth plugin directly instead of dynamic install

Remove dynamic installation of built-in plugins. GitLab auth is now imported

directly as an internal plugin, eliminating network requests during startup

and simplifying the plugin loading logic.

Removes the need for test mocks since plugins are no longer

dynamically installed at runtime.

packages/opencode/test/provider/provider.test.ts

@@ -1,27 +1,6 @@
-import { test, expect, mock } from "bun:test"
+import { test, expect } from "bun:test"
 import path from "path"
 
-// Mock BunProc and default plugins to prevent actual installations during tests
-mock.module("../../src/bun/index", () => ({
-  BunProc: {
-    install: async (pkg: string, _version?: string) => {
-      // Return package name without version for mocking
-      const lastAtIndex = pkg.lastIndexOf("@")
-      return lastAtIndex > 0 ? pkg.substring(0, lastAtIndex) : pkg
-    },
-    run: async () => {
-      throw new Error("BunProc.run should not be called in tests")
-    },
-    which: () => process.execPath,
-    InstallFailedError: class extends Error {},
-  },
-}))
-
-const mockPlugin = () => ({})
-mock.module("opencode-copilot-auth", () => ({ default: mockPlugin }))
-mock.module("opencode-anthropic-auth", () => ({ default: mockPlugin }))
-mock.module("@gitlab/opencode-gitlab-auth", () => ({ default: mockPlugin }))
-
 import { tmpdir } from "../fixture/fixture"
 import { Instance } from "../../src/project/instance"
 import { Provider } from "../../src/provider/provider"