build(examples): add justfile for sample-app

Targets: install/uninstall the APK, build the uatu CLI, run 'uatu test'
against a named AVD, run the Go verify tests, and clean. Keeps the
example self-contained so users can 'just test AVD=pixel_7' after cloning.

examples/sample-app/justfile

@@ -0,0 +1,48 @@
+set shell := ["bash", "-cu"]
+
+repo_root := absolute_path(justfile_directory() / ".." / "..")
+uatu      := env_var_or_default("UATU", repo_root / "bin/uatu")
+avd       := env_var_or_default("AVD", "")
+duration  := env_var_or_default("DURATION", "1m")
+seed      := env_var_or_default("SEED", "0")
+output    := env_var_or_default("OUTPUT", repo_root / "runs")
+
+default:
+    @just --list
+
+# Build and install the sample APK on a running emulator/device.
+install:
+    cd {{repo_root}} && ./gradlew :sample-app:installDebug
+
+# Remove the sample APK from the connected device.
+uninstall:
+    cd {{repo_root}} && ./gradlew :sample-app:uninstallDebug
+
+# Build the uatu CLI (writes to repo's bin/uatu).
+uatu:
+    make -C {{repo_root}} uatu
+
+# Run the Go tests that bundle and exercise spec.ts (no device required).
+verify:
+    cd {{repo_root}} && go test ./internal/verifier/ -run TestSampleAppSpec
+
+# Run 'uatu test' against the sample app. AVD=<name> is required.
+test:
+    #!/usr/bin/env bash
+    set -euo pipefail
+    if [[ -z "{{avd}}" ]]; then
+      echo "AVD is required (usage: just AVD=<name> test)" >&2
+      exit 1
+    fi
+    if [[ ! -x "{{uatu}}" ]]; then just uatu; fi
+    "{{uatu}}" test \
+      --spec "{{justfile_directory()}}/spec.ts" \
+      --bundle-id dev.uatu.sample \
+      --avd "{{avd}}" \
+      --duration "{{duration}}" \
+      --seed "{{seed}}" \
+      --output "{{output}}"
+
+# Remove the gradle build directory for the sample app.
+clean:
+    cd {{repo_root}} && ./gradlew :sample-app:clean