JCenter has been sunset and causes build failures. Replaced with mavenCentral().

Changes

• android/build.gradle: Replaced jcenter() with mavenCentral() in both buildscript and rootProject.allprojects repository blocks

buildscript {
    repositories {
        google()
-       jcenter()
+       mavenCentral()
    }
}

rootProject.allprojects {
    repositories {
        google()
-       jcenter()
+       mavenCentral()
    }
}

Fixes #125

This pull request was created as a result of the following prompt from Copilot chat.

Remove jcenter() repository references from android/build.gradle since JCenter has been sunset and can lead to build failures. Replace it with mavenCentral() in all repository blocks. See #125 for the related issue.

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