Fix F-Droid bot feedback issues [skip ci]

- Move fastlane metadata to repository root (was in android/fastlane)
- Add distributionSha256Sum to gradle-wrapper.properties for security
- Update Gradle Wrapper JAR to match version 8.13
- Document NonFreeNet anti-feature (HTTP support for local WebDAV servers)

Addresses F-Droid RFP issue #3458 bot feedback

android/gradle/wrapper/gradle-wrapper.properties

@@ -1,6 +1,6 @@
-#Sat Dec 20 00:06:31 CET 2025
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
+distributionSha256Sum=20f1b1176237254a6fc204d8434196fa11a4cfb387567519c61556e8710aed78
 distributionUrl=https\://services.gradle.org/distributions/gradle-8.13-bin.zip
 networkTimeout=10000
 validateDistributionUrl=true