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/runner/runner_test.go

@@ -321,10 +321,7 @@ func TestRunner_StampsHierarchyResolvedBoundsAndResiduals(t *testing.T) {
 	state.startSDK(t)
 	state.acceptConnection(t)
 
-	state.mock.HierarchyJSON = `<?xml version="1.0"?>
-<hierarchy>
-  <node resource-id="com.fixture:id/next" clickable="true" enabled="true" bounds="[40,80][240,160]"/>
-</hierarchy>`
+	state.mock.HierarchyJSON = `{"attributes":{"resource-id":"com.fixture:id/next","bounds":"[40,80,240,160]"},"children":[],"clickable":true,"enabled":true}`
 
 	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
 	defer cancel()