fix(runner): surface focus-tap errors in InputText (#12)

* fix(runner): surface focus-tap errors in InputText action

A failed Tap/TapSelector before InputText was swallowed, so text typed
into the wrong field (or no field) still reported success. Return the
error so the step fails explicitly.

* feat(sample-app): add username EditText and snapshot

Gives the spec a real EditText target (content-desc: username_field)
so the InputText action path can be exercised end-to-end. The typed
value is mirrored into MainActivity.username and surfaced as the
"username" snapshot for spec assertions.

* feat(sample-app): exercise InputText action against username field

Adds typeUsername action and usernameNeverShrinks property to the
sample spec, and extends the integration test to assert the bundled
spec emits an InputText(desc:username_field, "alice") action and that
the property correctly violates when a snapshot reports a shorter
string.

examples/sample-app/android/src/main/kotlin/dev/uatu/sample/MainActivity.kt

@@ -3,14 +3,18 @@ package dev.uatu.sample
 import android.app.Activity
 import android.graphics.Color
 import android.os.Bundle
+import android.text.Editable
+import android.text.TextWatcher
 import android.view.Gravity
 import android.widget.Button
+import android.widget.EditText
 import android.widget.LinearLayout
 import android.widget.TextView
 
 class MainActivity : Activity() {
     companion object {
         @Volatile var clickCount: Int = 0
+        @Volatile var username: String = ""
     }
 
     private lateinit var label: TextView
@@ -43,6 +47,29 @@ class MainActivity : Activity() {
         }
         layout.addView(button)
 
+        val usernameLabel = TextView(this).apply {
+            text = "Username: "
+            textSize = 20f
+            setTextColor(Color.BLACK)
+            gravity = Gravity.CENTER
+        }
+        layout.addView(usernameLabel)
+
+        val usernameField = EditText(this).apply {
+            hint = "username"
+            contentDescription = "username_field"
+            textSize = 18f
+            addTextChangedListener(object : TextWatcher {
+                override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) {}
+                override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) {}
+                override fun afterTextChanged(s: Editable?) {
+                    username = s?.toString() ?: ""
+                    usernameLabel.text = "Username: $username"
+                }
+            })
+        }
+        layout.addView(usernameField)
+
         setContentView(layout)
     }
 }

examples/sample-app/android/src/main/kotlin/dev/uatu/sample/SampleApplication.kt

@@ -9,6 +9,7 @@ class SampleApplication : Application() {
         Uatu.start(this)
         Uatu.extract("app_state") { "running" }
         Uatu.extract("click_count") { MainActivity.clickCount }
+        Uatu.extract("username") { MainActivity.username }
         Uatu.extract("uptime_millis") { System.currentTimeMillis() - startedAt }
     }