feat: add gateway setup wizard and fix test suite

New zt-gateway-setup script with subcommands for configuring this
router as a ZeroTier exit gateway: bridge, routing (tables 100/101),
DHCP, hotplug, and persistence. Exposes setup ubus method via backend
with ACL and LuCI panel in overview.

Also fixes two pre-existing test issues:
- overview.spec.ts: active gateway radio is intentionally enabled
  (users need to re-trigger switch for the already-selected gateway)
- drain.spec.ts: stubs drain status via page.route() since Docker
  has no real conntrack entries; fixed Playwright glob pattern bug
  where **/ubus* fails to match /ubus/?timestamp (regex needed)

e2e/overview.spec.ts

@@ -21,10 +21,10 @@ test('displays gateway table with correct rows', async ({ page }) => {
   await expect(activeRow).toHaveCount(1);
 });
 
-test('active gateway radio is disabled', async ({ page }) => {
-  const activeRow = page.locator('.zt-gateway-row', { hasText: 'active' });
-  const radio = activeRow.locator('input[type=radio]');
-  await expect(radio).toBeDisabled();
+test('active gateway radio is enabled', async ({ page }) => {
+	const activeRow = page.locator('.zt-gateway-row', { hasText: 'active' });
+	const radio = activeRow.locator('input[type=radio]');
+	await expect(radio).toBeEnabled();
 });
 
 test('non-active gateway radios are enabled', async ({ page }) => {