refactor(android)!: restructure to standard Capacitor plugin layout

Restructure Android project from nested module layout to standard
Capacitor plugin structure following community conventions.

Structure Changes:
- Move plugin code from android/plugin/ to android/src/main/java/
- Move test app from android/app/ to test-apps/android-test-app/app/
- Remove nested android/plugin module structure
- Remove nested android/app test app structure

Build Infrastructure:
- Add Gradle wrapper files (gradlew, gradlew.bat, gradle/wrapper/)
- Transform android/build.gradle from root project to library module
- Update android/settings.gradle for standalone plugin builds
- Add android/gradle.properties with AndroidX configuration
- Add android/consumer-rules.pro for ProGuard rules

Configuration Updates:
- Add prepare script to package.json for automatic builds on npm install
- Update package.json version to 1.0.1
- Update android/build.gradle to properly resolve Capacitor dependencies
- Update test-apps/android-test-app/settings.gradle with correct paths
- Remove android/variables.gradle (hardcode values in build.gradle)

Documentation:
- Update BUILDING.md with new structure and build process
- Update INTEGRATION_GUIDE.md to reflect standard structure
- Update README.md to remove path fix warnings
- Add test-apps/BUILD_PROCESS.md documenting test app build flows

Test App Configuration:
- Fix android-test-app to correctly reference plugin and Capacitor
- Remove capacitor-cordova-android-plugins dependency (not needed)
- Update capacitor.settings.gradle path verification in fix script

BREAKING CHANGE: Plugin now uses standard Capacitor Android structure.
Consuming apps must update their capacitor.settings.gradle to reference
android/ instead of android/plugin/. This is automatically handled by
Capacitor CLI for apps using standard plugin installation.

android/gradlew

@@ -15,6 +15,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 #
+# SPDX-License-Identifier: Apache-2.0
+#
 
 ##############################################################################
 #
@@ -55,7 +57,7 @@
 #       Darwin, MinGW, and NonStop.
 #
 #   (3) This script is generated from the Groovy template
-#       https://github.com/gradle/gradle/blob/HEAD/subprojects/plugins/src/main/resources/org/gradle/api/internal/plugins/unixStartScript.txt
+#       https://github.com/gradle/gradle/blob/HEAD/platforms/jvm/plugins-application/src/main/resources/org/gradle/api/internal/plugins/unixStartScript.txt
 #       within the Gradle project.
 #
 #       You can find Gradle at https://github.com/gradle/gradle/.
@@ -84,7 +86,8 @@ done
 # shellcheck disable=SC2034
 APP_BASE_NAME=${0##*/}
 # Discard cd standard output in case $CDPATH is set (https://github.com/gradle/gradle/issues/25036)
-APP_HOME=$( cd "${APP_HOME:-./}" > /dev/null && pwd -P ) || exit
+APP_HOME=$( cd -P "${APP_HOME:-./}" > /dev/null && printf '%s
+' "$PWD" ) || exit
 
 # Use the maximum available, or set MAX_FD != -1 to use that value.
 MAX_FD=maximum