Build AUR source packages against their own Gradle home, not offline

Both source PKGBUILDs ran "./gradlew --offline" against the builder's
personal ~/.gradle. That only worked as long as the local cache happened to
hold every dependency; the SpotBugs plugin 6.5.12 added in #114 broke
"yay -S kst4contest-git" with "could not resolve plugin artifact".

- drop --offline and point GRADLE_USER_HOME into $srcdir, so the package
  builds the same on any machine
- run with --no-daemon so no Gradle process outlives makepkg
- drop gradle from makedepends: the wrapper fetches its own distribution

Verified with makepkg -f on an empty Gradle home for kst4contest-git.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packaging/aur/kst4contest-git/PKGBUILD

@@ -7,7 +7,7 @@ arch=('x86_64')
 url="https://github.com/praktimarc/kst4contest"
 license=('GPL-3.0-only')
 depends=('gst-plugins-base' 'gst-plugins-good')
-makedepends=('java-environment=21' 'gradle' 'git')
+makedepends=('java-environment=21' 'git')
 provides=('kst4contest')
 conflicts=('kst4contest' 'kst4contest-bin')
 source=("kst4contest::git+https://github.com/praktimarc/kst4contest.git")
@@ -26,7 +26,12 @@ build() {
     export JAVA_HOME=$(find /usr/lib/jvm -maxdepth 1 -name 'java-21-*' -type d | head -n 1)
     export PATH="${JAVA_HOME}/bin:${PATH}"
 
-    ./gradlew --offline -S :app-desktop:createDistributable
+    # A Gradle home inside $srcdir keeps the build independent of whatever the
+    # builder's ~/.gradle happens to hold: with --offline against the personal
+    # cache, every dependency added since the last local build broke the package.
+    export GRADLE_USER_HOME="${srcdir}/gradle-home"
+
+    ./gradlew --no-daemon -S :app-desktop:createDistributable
 
     # package() reads dist/KST4Contest. Application name, icon and the JDK
     # module list come from app-desktop/build.gradle.kts.