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/hierarchies_test.go

@@ -1,19 +1,19 @@
 package verifier
 
-const listHierarchyXML = `<?xml version="1.0" encoding="UTF-8"?>
-<hierarchy rotation="0">
-  <node index="0" class="android.widget.FrameLayout" package="test.app" bounds="[0,0][1080,2400]">
-    <node index="0" class="android.widget.TextView" text="Items" bounds="[100,200][900,300]" />
-    <node index="1" class="android.view.View" content-desc="primary_action" clickable="true" enabled="true" bounds="[64,2200][1016,2320]" />
-    <node index="2" class="android.view.View" content-desc="secondary_action" clickable="true" enabled="true" bounds="[980,80][1060,160]" />
-  </node>
-</hierarchy>`
+const listHierarchyJSON = `{
+  "attributes": {"class": "android.widget.FrameLayout", "package": "test.app", "bounds": "[0,0,1080,2400]"},
+  "children": [
+    {"attributes": {"class": "android.widget.TextView", "text": "Items", "bounds": "[100,200,900,300]"}, "children": []},
+    {"attributes": {"content-desc": "primary_action", "bounds": "[64,2200,1016,2320]"}, "children": [], "clickable": true, "enabled": true},
+    {"attributes": {"content-desc": "secondary_action", "bounds": "[980,80,1060,160]"}, "children": [], "clickable": true, "enabled": true}
+  ]
+}`
 
-const formHierarchyXML = `<?xml version="1.0" encoding="UTF-8"?>
-<hierarchy rotation="0">
-  <node index="0" class="android.widget.FrameLayout" package="test.app" bounds="[0,0][1080,2400]">
-    <node index="0" class="android.view.View" content-desc="text_field" clickable="true" enabled="true" bounds="[64,320][1016,440]" />
-    <node index="1" class="android.view.View" content-desc="primary_action" clickable="true" enabled="true" bounds="[64,2200][1016,2320]" />
-    <node index="2" class="android.view.View" content-desc="secondary_action" clickable="true" enabled="true" bounds="[32,80][112,160]" />
-  </node>
-</hierarchy>`
+const formHierarchyJSON = `{
+  "attributes": {"class": "android.widget.FrameLayout", "package": "test.app", "bounds": "[0,0,1080,2400]"},
+  "children": [
+    {"attributes": {"content-desc": "text_field", "bounds": "[64,320,1016,440]"}, "children": [], "clickable": true, "enabled": true},
+    {"attributes": {"content-desc": "primary_action", "bounds": "[64,2200,1016,2320]"}, "children": [], "clickable": true, "enabled": true},
+    {"attributes": {"content-desc": "secondary_action", "bounds": "[32,80,112,160]"}, "children": [], "clickable": true, "enabled": true}
+  ]
+}`