feat: Maestro driver integration + DeviceDriver architecture (#32)

* proto(driver): drop launcher_activity from LaunchRequest

* refactor(driver): rename Driver to DeviceDriver, drop launcherActivity from Launch

* refactor(driver): rename package maestro to sidecar

* feat(driver): add ChromeDriver backed by chromedp

* feat(hierarchy): replace XML parser with TreeNode JSON parser

* refactor(driver): update mock and runner to DeviceDriver, drop launcherActivity

* feat(runner): add platform routing for web vs sidecar

* test(verifier): update hierarchy fixtures from XML to TreeNode JSON

* feat(sidecar): extract readLogcat/readProcMetrics; add MaestroDriverBackend

- Extract readLogcat() and readProcMetrics() as internal package-level
  helpers parameterised by serial
- Add MaestroDriverBackend wiring maestro-client AndroidDriver
- Drop launcherActivity from DriverBackend interface and StubDriverBackend
- Add maestro-utils and micrometer-core as explicit compile deps

* refactor(sidecar): inject DriverBackend into DriverService; drop launcherActivity

- Remove serial and default backend from DriverService constructor
- Make backend a required parameter
- Drop launcherActivity from launch RPC handler
- Create MaestroDriverBackend in Main.kt when platform is android

* test(sidecar): update tests for dropped launcherActivity and required backend

* chore(sidecar): remove unnecessary micrometer-core direct dependency

internal/driver/mock/mock_test.go

@@ -29,7 +29,7 @@ func TestRecordsAllActionsInOrder(t *testing.T) {
 	mock := New()
 	ctx := context.Background()
 
-	if err := mock.Launch(ctx, "com.example", "com.example/.MainActivity", true); err != nil {
+	if err := mock.Launch(ctx, "com.example", true); err != nil {
 		t.Fatal(err)
 	}
 	if err := mock.Tap(ctx, 100, 200); err != nil {
@@ -137,5 +137,5 @@ func TestActionsReturnsCopy(t *testing.T) {
 }
 
 func TestSatisfiesDriverInterface(t *testing.T) {
-	var _ driver.Driver = New()
+	var _ driver.DeviceDriver = New()
 }