fix(tests): update E2E exit code assertions for usage errors

Argument/usage errors now correctly exit with code 2 (EX_USAGE) since
the exit-codes feature landed. Update the two affected E2E assertions:
- unknown command → 2 (usage error, not generic failure)
- plugin update without args → 2 (ArgumentError)

tests/e2e/management.test.ts

@@ -101,6 +101,6 @@ describe('management commands E2E', () => {
   // ── unknown command ──
   it('unknown command shows error', async () => {
     const { stderr, code } = await runCli(['nonexistent-command-xyz']);
-    expect(code).toBe(1);
+    expect(code).toBe(2);
   });
 });

tests/e2e/plugin-management.test.ts

@@ -134,7 +134,7 @@ describe('plugin management E2E', () => {
 
   it('plugin update without name or --all shows error', async () => {
     const { stderr, code } = await runPluginCli(['plugin', 'update']);
-    expect(code).toBe(1);
+    expect(code).toBe(2);
     expect(stderr).toContain('specify a plugin name');
   });
 });