Fix Android emulator app launch

Three issues prevented `run_android_emulator.sh` from launching the app:

- gradlew's shebang was a hardcoded Nix-store bash path (copied verbatim
  from the nixpkgs Flutter SDK template) that breaks once that store path
  is garbage-collected, surfacing as a misleading "ProcessException: No
  such file or directory". The dev-shell now normalizes the gitignored
  android/gradlew shebang to the portable "#!/usr/bin/env sh" on entry.
- `flutter run -d android` never matched: -d resolves a device by id/name,
  not platform. Resolve the concrete id (e.g. emulator-5554) from
  `flutter devices --machine` instead.
- Install raced the boot ("device is still booting"); wait for
  sys.boot_completed=1 before launching.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/run_android_emulator.sh

@@ -15,15 +15,50 @@ if ! command -v flutter >/dev/null 2>&1; then
   exit 1
 fi
 
+# Print the id of the first connected Android device, or nothing if none is up.
+# `flutter run -d <x>` matches a device by id/name, never by platform, so the
+# literal "android" is not a usable target; we must resolve the concrete id
+# (e.g. "emulator-5554") from flutter's own machine-readable device list.
+android_device_id() {
+  flutter devices --machine 2>/dev/null | python3 -c '
+import json, sys
+try:
+    devices = json.load(sys.stdin)
+except ValueError:
+    devices = []
+for d in devices:
+    if str(d.get("targetPlatform", "")).startswith("android"):
+        print(d["id"])
+        break
+'
+}
+
+# Block until the Android OS on the given device has finished booting. The
+# device shows up in `flutter devices` as soon as adb connects, but installing
+# before boot completes fails with "device is still booting", so we poll the
+# sys.boot_completed property (adb shell emits CRLF, hence the trailing-\r trim).
+wait_for_boot() {
+  local serial="$1"
+  adb -s "$serial" wait-for-device
+  until [ "$(adb -s "$serial" shell getprop sys.boot_completed 2>/dev/null | tr -d '\r')" = "1" ]; do
+    sleep 2
+  done
+}
+
 # Boot the emulator in the background if no Android device is connected yet.
-if ! flutter devices 2>/dev/null | grep -qi "android"; then
+if [ -z "$(android_device_id)" ]; then
   echo "No Android device detected, booting the emulator..."
   "$SCRIPT_DIR/run_android.sh" -no-snapshot-save &
 
   echo "Waiting for the emulator to come online..."
-  until flutter devices 2>/dev/null | grep -qi "android"; do
+  until [ -n "$(android_device_id)" ]; do
     sleep 2
   done
 fi
 
-exec flutter run -d android "$@"
+device_id="$(android_device_id)"
+echo "Waiting for '$device_id' to finish booting..."
+wait_for_boot "$device_id"
+
+echo "Launching OOTT on '$device_id'..."
+exec flutter run -d "$device_id" "$@"