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/verifier/ax_integration_test.go

@@ -9,12 +9,13 @@ import (
 
 // TestStateAxFindWorks verifies that a Parse+PushSnapshot+extract round trip
 // actually lets the spec resolve selectors through state.ax.find.
+// Reads /tmp/live-dump.json (Maestro TreeNode JSON format); skipped if absent.
 func TestStateAxFindWorks(t *testing.T) {
-	xmlText, err := os.ReadFile("/tmp/live-dump.xml")
+	jsonText, err := os.ReadFile("/tmp/live-dump.json")
 	if err != nil {
-		t.Skip("live-dump.xml not present")
+		t.Skip("live-dump.json not present")
 	}
-	tree, err := hierarchy.Parse(string(xmlText))
+	tree, err := hierarchy.Parse(string(jsonText))
 	if err != nil {
 		t.Fatal(err)
 	}